reference will now be made in detail to several embodiments of the invention that are illustrated in the accompanying drawings . wherever possible , same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps . the drawings are in simplified form and are not to precise scale . for purposes of convenience and clarity only , directional terms , such as top , bottom , inner , outer , above , below , beneath , rear , and front may be used with respect to the drawings . these and similar directional terms should not be construed to limit the scope of the invention in any manner . the words “ connect ,” “ couple ,” and similar terms with their inflectional morphemes do not necessarily denote direct and immediate connections , but also include connections through mediate elements or devices . additionally , the terms “ brush ” and “ brush unit ” are used interchangeably . referring more particularly to the drawings , fig1 and 1 a illustrate an assembled brush unit 10 configured with a housing 12 . while the housing is illustrated as having a dome - like shape , it can have a variety of shapes subject only to ergonomic requirements . for example , the housing has to fit comfortably the user &# 39 ; s hand . furthermore , it is desirable that the dimensions of housing 12 are so selected that the housing is neither too small nor too large . preferably , the upper surface of housing 12 extends along the entire length of the user &# 39 ; s palm and terminates under the user &# 39 ; s fingers adjacent to a bladder 24 . turning to fig2 a - 2g , 3 and 5 in addition to fig1 and 1 a , fluid selected from the group , which may include , but are not limited to , shampoo , hair conditioner , flea treatment , soap and / or dishwashing liquid , is delivered into housing 12 through an inlet port 14 . inlet port 14 may be variously shaped and dimensioned . preferably , inlet port 14 includes a circular opening provided in a flange 26 ( fig1 a ), which extends outwards from housing 12 . an outer wall 17 ( fig1 a ) of flange 26 may threadingly engage an inner thread of a lid 16 , which , thus , can be detachably coupled to flange 26 . alternatively , dimensions of lid 16 and flange 26 may be selected so that lid 16 is pushed onto flange 26 for a tight fit thus eliminating the need for threads on the opposing surfaces of flange 26 and lid 16 , respectively . other types of connection , such as a bayonet connection , are also contemplated within the scope of this invention . lid 16 and flange 26 are configured to be removably coupled to one another in a fluidproof manner for preventing voluntary escape of fluid from housing 12 regardless of the position of brush unit 10 . lid 16 includes a cup - shaped body 28 ( fig2 b , 3 ) formed with a central opening 28 a configured to receive bladder 24 made from flexible material . the outer diameter of the bladder 24 is slightly greater than the diameter of the central opening . as a consequence , bladder 24 , when pushed through the opening of a ring - shaped body 28 of lid 16 , tightly fits the peripheral wall of opening 28 a in a manner preventing fluid from escaping housing 12 . to ensure imperviousness of lid 16 , the bladder is provided with a radial lip 25 ( fig3 ) pressing against an underside 27 of lid 16 upon attaching the bladder to the lid . as mentioned above , bladder 24 is disposed over inlet port 14 that in turn is preferably positioned under the user &# 39 ; s fingers . the user presses bladder 24 whenever a situation requires an additional amount of fluid . the interior of housing 12 is formed as a chamber in fluid communication with inlet port 14 for receiving and storing fluid . housing 12 may be formed as a one - piece component with the chamber defined by the inner peripheral surface of the housing &# 39 ; wall between the dome - shaped top and bottom of the housing . in accordance with a further modification , housing 12 is configured with two housing portions 20 and 60 ( fig2 - 3 ), only one of which is formed with the inlet port 14 and the chamber . base portion 60 of housing 12 is configured with a bottom 62 ( fig2 a ) and a top 64 ( fig2 b ). top 64 does not continuously cover the entire bottom 62 , but has a cutout region 30 ( fig2 c ). top 64 is so cutout that a front area 66 of the bottom 62 ( fig2 b ) has a flange 68 ( fig2 c , 3 ) extending upwards from the bottom and along the periphery of the entire front area 66 . accordingly , base portion 60 has an inner surface including the inner side of flange 68 and the underside of top 64 . hollow portion 20 of the housing is configured so that , upon coupling portions 20 and 60 , the outer surface of portion 20 smoothly extends from the outer surface of top 64 and flange 68 of base portion 60 ( fig3 ) without steps or substantial gaps . the inner surface of hollow portion 20 is substantially continuous except for a flange 70 ( fig2 e , 3 ) provided in the bottom of portion 20 and the opening provided within flange 26 and defining inlet port 14 . thus , the interior of portion 20 defines a chamber for receiving and storing fluid . flange 70 opening into the chamber and extending downwards from the bottom of portion 20 has an inner surface defining a passage for fluid that is forced through the outlet port . housing portions 20 and 60 may be coupled in numerous ways . for example , the geometry of the peripheral wall of portion 20 may be configured so that a region 32 ( fig2 d ) connecting the top and rear wall of portion 20 engages a receiving surface of the top 64 of base portion 60 . similarly , a bottom edge 36 ( fig3 ) of the peripheral wall of portion 20 frictionally slides against a receiving surface of the flange 68 of base portion 60 . pushing housing portions 20 and 60 towards one another provides reliable engagement between the contacting surfaces of the housing portions . as a result , the housing 12 has a smooth outer surface conveniently fitting the hand of the user while using brush 10 . alternatively , opposing surfaces of housing portions 20 and 60 may be provided with a plurality of matching projections and recesses . for example , portion 20 may have a plurality of spaced apart projections configured to frictionally move into respective recesses formed on the peripheral edge of base portion 60 . conversely , the projections can be provided on base portion 60 , whereas the recesses are located on portion 20 . flange 70 , provided in the top portion 20 , is aligned with and extends through a hole 76 ( fig2 f ) formed in front area 66 of bottom 62 of base portion 60 . hole 76 is somewhat larger than the outer diameter of flange 70 and , thus , defines a groove 77 ( fig3 ) within bottom 62 of base portion 60 configured to receive an inner end of the cover for a valve assembly , as will be explained in detail hereinafter . housing 12 is completed with a tray 78 ( fig2 b ) juxtaposed with and coupled to the outer side of the bottom 62 of the housing base portion 60 . tray 78 is configured so that its edge 37 surrounds the bottom of base portion 60 and forms a continuous peripheral ledge 34 ( fig3 ) extending laterally outwards from housing 12 . preferably , the brush 10 is made from various polymeric materials . accordingly , using numerous molding techniques , base portion 60 and tray 78 may be manufactured as a unitary part , or , of course , these components may be manufactured separately and later coupled to one another , as shown in fig2 a . tray 78 has a respective hole 38 ( fig2 b ) aligned with flange 70 and having an inner diameter substantially the same as hole 76 of bottom 62 of the housing &# 39 ; s base portion 60 . a brush head 82 ( fig2 g , 3 ) is coupled to housing 12 and has a plurality of bristles 84 . to complete the outlet port of brush 10 , brush head 82 is provided with a hole 86 also aligned with the holes of the housing 12 during assembly of the brush 10 . the brush head 82 may be removably attached to the housing 12 . due to its elasticity , the brush head may be stretched over ledge 84 so that flange 88 ( fig3 ) is engaged with ledge 34 formed by edge 37 of tray 78 . to prevent brush head 82 from dislodging during usage , the opposing surfaces of brush head 82 and tray 78 may be glued together . alternatively , the inner side of brush head 82 may have one or a plurality of suction cups engaging the opposing outer surface of tray 78 . furthermore , brush head 82 may be simply screwed on housing 12 . preferably , all components of brush unit 10 are made from polymeric materials , such as engineering plastics , rubber and the like . however , the modulus of elasticity of materials used for manufacturing different components of brush 10 is not uniform . for example , housing 12 may be made from rigid polymeric materials incapable of yielding to loads produced by the user . bladder 16 and brush head 82 , in turn , are composed of flexible polymeric materials , such as rubber . however , the brush head may be made from relatively rigid polymeric material . housing portion 20 configured with fluid chamber is preferably made from transparent polymeric materials allowing the user to observe the level of fluid in the chamber . furthermore , the use of differently colored materials enhancing the aesthetic appeal of brush 10 is also envisioned within the scope of the invention dispensing of fluid from housing 12 through the outlet port is realized by a valve assembly 100 detachably coupled to the outlet port of housing 12 . referring to fig4 , valve assembly 100 includes a valve member 44 , a holder 50 and a cover 90 . valve assembly 100 is installed by initially placing valve member 44 into holder 50 . then , the assembled holder / valve unit is inserted through the outer end of flange 70 of the housing portion 20 . flange 70 and holder 50 are dimensioned so that upon insertion of the holder , their inner or top end are substantially flush with the inner surface of the bottom of housing portion 20 , whereas the bottom or outer end of holder 50 is received within a seat formed in the outer discharge end of flange 70 ( fig3 ). once the assembled holder / membrane unit is placed within flange 70 , cover 90 is screwed onto the outer surface of flange 70 to prevent displacement of the valve unit from housing 12 . as the inner threaded surface of cover 90 engages the threaded outer surface of flange 70 , the inner end of the cover moves within a groove 77 ( fig3 ) formed in the bottom of base portion 60 . displacement of the cover continues until its inner or top end abuts the outer side of the bottom of housing portion 20 . instead of screwing cover 90 , it is possible to select dimensions of the cover and flange 70 so that the cover simply slides along the flange in a manner preventing its voluntary displacement in the opposite direction . holder 50 ( fig4 ) ( shown in an inverted position ) has a cup - shaped body and a rim 52 spaced from the top of holder 50 and extending radially outwards from the body . the top of holder 50 is provided with multiple angularly extending recesses 54 , which are separated from one another by a plurality of radially extending ribs 56 . valve member 44 is also provided with a cup - shaped body and a respective collar 40 juxtaposed with the underside of rim 52 of holder 50 upon insertion of valve member 44 into the holder . valve member 44 is dimensioned so that its top 42 is pressed against an underside 58 of the holder &# 39 ; s top and covers recesses 54 . at least one slit , but preferably a multiplicity of slits 46 , is formed in the top of valve member 44 defining , thus , at least two top segments 48 . due to the elasticity of the valve member , segments 48 are tightly attached to one another preventing fluid from escaping the chamber of housing portion 20 . however , once the pressure within the chamber is increased in response to an external pressure exerted upon the bladder 24 ( fig3 ), the top segments deflect from one another to define a passage for fluid therebetween . consequently , fluid exits an opening 92 formed in the bottom of cover 90 ( fig4 ). in accordance with a further aspect of the invention , a kit may be provided containing brush unit 10 and a plurality of brush heads 82 . each of the heads 82 may be used for a respective surface . dealing with animals , for example , bristles 84 may be relatively large for long - coat animals , whereas short - coat animals can be treated with relatively small bristles . furthermore , the bristles 84 may be arranged in different patterns and have different dimensions . the user may decide which one of the purchased heads is most suitable for any given surface and easily attach the desired head to housing 12 of brush unit 10 . the specific features described herein may be used in some embodiments , but not in others , without departure from the spirit and scope of the invention as set forth . many additional modifications are intended in the foregoing disclosure , and it will be appreciated by those of ordinary skill in the art that in some instances some features of the invention will be employed in the absence of a corresponding use of other features . the illustrative examples therefore do not define the metes and bounds of the invention .