in the following description , the expression &# 34 ; powder room &# 34 ; contemplates a water closet , toilet and the like , while the expression &# 34 ; bathroom &# 34 ; contemplates a full bathroom which may include a powder room and bathtub section -- with or without a shower -- in combination . the invention is comprised of five modular basic elements , segregated according to function . each element contains one or more prefabricated components and each component can be factory assembled to various degrees of completion , at option . accordingly the degree of in - field assembly can be varied as economics or local labor practices require . the five basic elements are : 2 . the wall surface interface frame 12 of the interface unit 30 . referring to fig1 there is illustrated a drain - waste - vent pipe unit 10 , sometimes referred to as a dwv stack . the drain - waste - vent pipe unit is an assemblage of drain - waste - vent pipes and fittings which are conventionally connected to the drain - waste - vent system of the building structure at end portions 20 and 22 and contains a drain waste and venting configuration as shown . it is installed in the piping chase of the &# 34 ; wet wall &# 34 ; of a room section of the building . according to normal practice , installation of this stack is generally accomplished at the time the rough plumbing of the building is installed with the only particular requirement being that the drain - waste - vent pipe unit is properly positioned in relation to the finished floor line and with a selected wall of the bathroom of powder room . this positioning is generally accomplished by means of a jig ( not shown ) and assures proper connection with the piping components of the system at the three open positions 24 , 26 , and 28 . the drain - waste - vent pipe unit 10 may be either factory of field assembled but must conform to specific dimension requirements to insure proper interconnection with the piping components of the drain - waste - vent piping system associated with the room and the building structure . certain variations of the drain - waste - vent pipe unit may be required for different applications . for example , one version of the type shown in fig1 is intended to be used with a single bathroom or powder room . a second version may be used for back - to - back bathrooms or powder rooms where interconnections must be made to pipe components on both sides of the &# 34 ; wet wall &# 34 ; or piping chase as will be seen in the description which follows . these multiple pipes are generally intended for structures such as high rise buildings in which powder rooms or bathrooms are positioned in back - to - back relation . however multiple installations would naturally require larger diameter vertical pipes to accommodate proportionately higher volume of waste . referring now to fig2 there is shown the component frame members and brackets of a structural unit 12 which upon assembly , form an interface core structure which supports the drain - waste - vent pipe unit and the drain - waste - vent piping system associated with the room . the interface structure is comprised of three major elements and forms the basic template for a full bathroom when assembled and installed in a room as shown in fig6 . the three major elements shown in fig2 comprise templates 14 for the bathtub section , 16 for the toilet section , and 18 for the vanity sink section . alternately , by merely eliminating the bath section , the basic interface core provides a template for a powder room . the interface frame sections are rigid members which may be factory assembled or assembled in - situ to form a planar frame to conform it to the particular requirements of a specific installation . the conponents of the structure are preferably fabricated of a metal such as steel , iron , brass , etc . however , the frame may be of plastic materials since most of the in - room elements are floor supported and the only strength required in the frame must be sufficient to support the interface piping and to secure the positioning of in - room elements . the elements of the frame structure may be secured together by threadedly engaging the components , or by bolts , screws and the like , but are preferably assembled by telescoping the sections and securing them with screws , bolts , clamps , etc . or by a snap - together arrangement . referring now to fig3 the structural interface frame 12 of fig2 is shown in assembled form 30 with the drain - waste - vent piping system 32 through 52 secured in position . the assembly shown in fig3 is suitable for use in a full bathroom ( ie . bathtub section , toilet section and vanity sink section ). as can be seen in the drawings , the drain - waste - vent interface unit 30 provides a convenient layout of the bathroom of powder room with dimensions conforming to the requirements of the particular room in which the installation is to be made . fig4 is a side view of the interface unit of fig3 and illustrates a bathtub support 54 which supports the forward portion of the bathtub as will be seen in the description which follows . referring now to fig5 there is shown an unfinished room 55 framed with studs 56 in which the drain - waste - vent pipe unit 10 of fig1 is installed and connected to the drain - waste - vent piping chase of the wet wall of the room section of the building structure . the drain - waste - vent pipe unit must be positioned with the &# 34 ; wet wall &# 34 ; of the building as shown -- prior to any other installations -- the dimensional position requirements with respect to the finished room strictly adhered to as previously noted . referring to fig6 there is illustrated the room 55 of fig5 with the interface unit 30 of fig3 floor supported and installed in adjoining relation to the wet wall 58 . it is secured to the &# 34 ; wet wall &# 34 ; by conventional securing means such as nails , screws , etc ., preferably with the bathtub end of the frame in contact with the tub wall studs or rough wall . this assures proper alignment of the three interconnections between the interface piping and the drain - waste - vent pipe unit . for a powder room only , the interface unit will be secured in contact with the lavatory wall at the toilet end in which case proper alignment of the two interconnections will be assured . water supply lines 60 are installed and a shower riser pipe 62 , if required , is positioned adjacent the bathtub bracket 14 of the interface . a feature of the present invention resides in the capability of installing interface unit 30 -- or even the entire powder room or bathroom -- in position against the &# 34 ; wet wall &# 34 ; after the upper portion of the walls of the room have been completed and finished ( painted , wallpapered , etc .). the interface unit , being a surface mounted pre - piped unit -- which is not required to be integrally assembled as part of the basic structure of the room -- is thus suitable for original or prime installations or for powder room and bathroom conversions . the connections between the pipes and the drain - waste - vent pipe unit 10 are preferably of the type generally used with the pipes selected in a particular installation . for example , the pipes may be comprised of brass , iron , etc . accordingly , the pipe connections will be unions , elbows and the like , of iron or brass . copper pipes will be connected by connecting means generally used with such members such as sweated joint connections . also the hot and cold water supply lines 60 to each fixture may be of the type generally used according to local practice . for example , these lines may be the form of copper tubing sweated to the supply piping of the system . referring further to fig6 an electrical junction box 66 is provided as part of the lavatory portion of the frame . this permits interconnection between the building wiring 68 and the room lighting , which -- as will be seen -- is attached to a medicine cabinet component of the modular lavatory section . wiring 70 from the junction box 66 extends to an electrical recepticle 72 located at the top center of the lavatory section of the interface frame . after completion of the installation as illustrated in fig6 the basic plumbing system is complete and in those geographical locations in which local rules may require , the plumbing ( local or other ) inspector may inspect and perform the necessary tests of the system with complete access to all components , connections and joints . thus in the event further work is required to comply with local codes and practices , this may be detected and corrected prior to proceeding further . the bathtub / shower section is comprised of four major components : the bathtub and a three - piece wall surround . the bathtub is a free standing , floor - supported unit with a factory fitting overflow drain assembly . it is so configured that it can be brought into a finished ( or a partially finished ) room , placed in position against the tub wall and the face of the interface unit bracket 54 , and then lowered to the floor . fig7 illustrates the installation shown in fig6 with the bathtub 74 of the present invention installed into position . the installation of the modular bathtub 74 of the present invention is peculiarly applicable to the present system as will be described in connection with fig8 and 9 . the bathtub 74 is positioned by the interface unit and secured in position by the three - piece wall surround . the forward portion 76 of the tub 74 engages the lip 54 of bracket 14 of the bathtub section of interface unit 30 . the bathtub 74 shown in fig7 is uniquely configured to have an elongate configuration with one arcuate end portion as shown . it may be constructed of conventional materials such as enamel iron , enameled steel , plastic materials , and the like . preferably the bathtub will be approximately 16 inches high so as to permit it to pass through a standard doorway 2 feet in width . it is approximately 30 inches wide in accordance with established standards for residential bathrooms and it is approximately 551 / 2 inches long and particularly configured to have a radiussed arcuate configuration along one of the shorter sides as shown in fig8 . the center of the radius of the arcuate side of the bathtub is preferably located approximately at the lower left hand corner portion 78 of forward portion 76 of the bathtub as shown in fig8 . with this configuration the bathtub can be simply fitted into the room after all heavy plumbing and structural work has been completed and then rotated snugly into position in the bathtub end of the room structure and supported on hanger rails 58 as shown in fig7 . thus with all structural and plumbing work completed prior to its installation , the risk of damage to the finished surface of the bathtub is minimized . this risk was generally substantially great in prior art installations during the performance of the structural and plumbing work in the room . for the same reasons the risk of damage to the remaining modular fixtures of the present invention is substantially eliminated . referring now to fig9 there is illustrated a side view of the lower forward end portion of the bathtub in which the bathtub drain fitting is connected to the drain - waste - vent system of the room . while it is preferred that the drain connection 80 is accomplished by a quick - connect clamping unit 82 , since certain local codes will not permit them , it is also contemplated within the scope of the present invention to connect the drain system of the bathtub by conventional means such as threaded pipes , unions , etc . ( not shown ). the opening 84 defined by the forward left - hand side wall of the bathtub 74 , is later covered by a shroud section of the modular toilet bowl as will be seen . the bathtub may be provided in left and right - hand versions to accommodate installations as shown , or installations having a &# 34 ; mirror image &# 34 ; of the installation shown . it is clear that the modular aspects of the present bathtub provide particular convenience in the installation , repair and / or replacement thereof . also , the combination of the wall surface mounted interface unit 30 , and the bathtub 74 may be installed within several hours thereby avoiding the high costs of labor which were normally incurred during comparable installations of the prior art . the forward open position of the bathtub of the present invention permits ready access for repairs as contrasted to prior art bathtubs in which leaks , for example , were generally so difficult to repair -- due to the inaccessibility of the drain supply connections to the tub -- that often the cost approached the cost of a new bathroom . in fig1 there is illustrated , the bathroom shown in fig9 with the first wall surround panel member 86 secured into position over the forward portion of the bathtub . the panel 86 is preferably secured in position by the shower head 62 which is threadedly engaged into the riser pipe system behind the panel in a manner which secures the panel against the structure as shown in fig1 . further securing of the wall surround 86 may be accomplished by rotating the threaded escutcheon 88 surrounding the shower - tub water supply lever 90 . the escutcheon 88 is threaded into a bathtub bracket attached to the interface frame 12 of interface unit 30 ( not shown ). referring further to fig1 there is illustrated a unique &# 34 ; tongue and groove &# 34 ; feature of the wall surround member 86 whereby the lower portion is spaced from the lower portion 94 of the bathtub / shower section 14 of the interface unit 12 to define a slotted lower portion surrounding a lip ( or ledge ) 98 of bathtub 74 . the ledge 98 engageably enters the slot defined by the lower portion of the surround to create a &# 34 ; water barrier &# 34 ; in the form of a water - tight seal about the periphery of the bathtub and acts to secure the bathtub in proper position , as described in connection with fig7 . referring now to fig1 , the interconnection between the second shower wall surround member 102 is secured in position similarly to wall surround member 86 . the third wall surround member 100 is positioned by a &# 34 ; tongue and groove &# 34 ; arrangement similar to the other wall surround members and the three wall surround members are locked in attached relation by &# 34 ; tongue and groove &# 34 ; arrangements at 104 and 106 . while the wall surround members 86 , 100 and 102 are partially secured in position against the studding or interface frame by screws or other fasteners 108 shown in fig1 , the final securing is accomplished by positioning a shower curtain rod 110 in position as shown in fig1 . the shower curtain rod is preferably adjustable in length such that it can be predimensioned to cause the wall surround members 86 and 102 to be secured in position while providing adjustments for minor dimensional variations in the studded walls . also , the tongue and groove interlocking system between wall surround members 86 and 100 and members 100 and 102 as described , securely maintain the relative positions of these members . it can be seen that at this point the basic components of the bathroom are assembled in predimensioned relation . the wall surround members 86 , 100 and 102 are uniquely locked into position as described , while providing a water tight seal along the periphery of the tub . the wall surround components may also be provided in right or left - hand versions . fig1 illustrates the bathroom shown in fig1 with the toilet section 108 installed in position and toilet bowl 110 connected with the drain waste and water supply system by pipping means shown in fig1 . water tank 112 is mounted to the interface unit 30 by an associated integral shroud unit 114 which is prefabricated , floor supported , and secured into position by means of towel bar brackets 116 and 118 as shown in fig1 . towel bar 120 is mounted to these brackets . the brackets 116 and 118 have securing means 124 which extend through the shroud 114 and are attached by suitable attachment means such as nuts 126 to secure the toilet section in position against interface unit 30 . the flush tank 112 is supplied with a conventional flush valve 122 and control valve and flushing actuating mechanism ( not shown ). a unique feature of the toilet bowl 110 of the present invention is clearly illustrated in the cross - sectional view of fig1 . by the provision of internal flush water and waste channels 128 and 130 , respectively -- which extend toward , and are opened to , the rearward face of the toilet bowl unit -- it is now possible to secure the toilet bowl for tank - type or pressure - type ( commercial ) flushing in a single step mounting operation . the toilet bowl 110 is floor - supported and mounted in adjacent relation and abutting with the shroud 114 of the toilet section . the bowl 110 is secured in position by merely threading two bolts 132 ( one bolt not shown in fig1 and 17 ) sufficient to secure the bowl 110 in position . referring once again to fig1 an outlet seal ring 134 of a bees wax - type is positioned between the outlet channel 130 of the toilet bowl and the waste pipe 136 which completes the waste line from the bowl to the drain - waste - vent pipe unit 10 through outlet 28 . thus by the provision of a rear water flush - rear waste outlet tank - type toilet bowl , it is possible to install the toilet bowl in position in a single attachment step thereby avoiding unnecessary and expensive labor costs generally incurred in installing systems of the prior art . a conventional toilet seat 138 may be provided is shown in fig1 . referring now to fig1 there is illustrated a perspective view of the completed bathroom of the present invention . the lavatory section 140 included wash basin 142 secured within a full standing vanity cabinet 144 having doors 146 and a lavatory counter top 148 . an upper interface shroud 150 is connected to the counter top 148 and is securely mounted to the vanity section as shown and is secured against the interface core unit by decorative accessories such as by threadedly attaching a soap dish 152 and glass and tooth brush holder 154 threaded into the interface unit frame behind the shroud in a manner similar to the attachment of the towel bar bracket attachment shown in fig1 . a securing member which forms part of these accessories extends through the shroud and is attached to a bracket member which is secured to the frame of the interface unit . once the lavatory section is mounted in position , supply and drain interconnections to the interface unit piping system are preferably completed by using quick flexible connectors ( not shown ) for water supplies and drains , or alternatively , conventional connecting means as may be required by local plumbing codes . room illumination may be provided by lights 156 and 158 ( fluorescent or other conventional types ) which comprise part of the medicine cabinet . the modular medicine cabinet 160 is properly positioned on the top ledge of the upper interface shroud 140 and secured to it by means of two bolts or screws . as it is positioned , an electrical plug engages the electrical receptacle 72 previously illustrated for providing power to the lights 156 and 158 . it can be seen from the foregoing description that the modular aspects of the wall mounted interface unit as well as the modular aspects of the fixtures of the washroom or full bathroom make it possible to install a bathroom or powder room in a substantially completed room while reducing the time and labor costs to assemble such facilities . there is illustrated in fig1 through 21 some of the various combinations and arrangements which are possible utilizing the present invention . moreover the interchangeable aspects of the components of the present invention make it possible to provide left hand and right hand powder rooms or full bathrooms as shown in fig1 through 21 . in fact , last minute changes from a full bathroom having a tub on the right hand side can be made to convert the arrangement to a full bathroom having the tub on the left hand side by a mere interchange of the tub section of the interface frame and subsequent installations . further , the tub can be completely eliminated to provided merely a powder room installation . the modular aspects of the present invention facilitate numerous combinations and arrangements of bathrooms , powder rooms and the like which will readily come to the minds of persons skilled in the art . in fig1 there is shown a single bathroom , while in fig1 there is illustrated a single powder room , while in fig2 there is illustrated a full bathroom and a powder room in back - to - back relation . the versatility and symmetry of the sections of the interface core makes it possible to assemble the modular components of the present invention so as to adapt them to individual needs while the modular aspects make it posible to market the components on a part - by - part basis , or as a complete system . thus it is now possible to market a powder or bathroom on a cash - and - carry basis while its installation can be completed in a new room or an existing room with a minimum amount of professional plumbing required .