depicted in fig1 a - b is exemplary scrubber 10 . scrubber 10 , which is generally similar to scrubbers of the van der meijden application , may include blades 14 and shaft 18 . also illustrated in fig1 a - b is hub 20 interconnecting blades 14 and shaft 18 . in use , scrubber 10 desirably rotates about shaft 18 so as to move water toward an inlet 21 of a cleaner such as apc 22 ( see fig5 ). when the apc 22 is upright on a bottom surface of a pool , shaft 18 will be generally perpendicular to the plane of the bottom surface and thus scrubber 10 will rotate about an axis perpendicular ( or generally so ) to the bottom surface . consistent with the discussion in the van der meijden application , blades 14 preferably are “ semi - rigid ” in nature , meaning that they have sufficient flexibility to accommodate passage into inlet 21 of apc 22 , without blockage , of at least some larger types of debris often found in outdoor swimming pools . the term “ semi - rigid ” also means that blades 14 nevertheless have sufficient rigidity to move volumes of water toward the inlet 21 of the cleaner as they rotate about shaft 18 . a presently - preferred material from which blades 14 is made remains molded thermoplastic polyurethane , although other materials may be used instead . scrubber 10 advantageously may include six blades 14 extending radially from shaft 18 . fewer or greater numbers of blades 14 may be employed as appropriate , however . as illustrated in fig5 , two scrubbers 10 preferably are employed as part of apc 22 , with each scrubber 10 being positioned at least partly to a side of inlet 21 of the apc 22 . again , though , fewer or greater numbers of scrubbers 10 may be utilized , and each or any scrubber 10 may be positioned in any suitable location . as shown in fig1 a , many of the six blades 14 are circumferentially spaced approximately forty - five degrees , rather than approximately sixty degrees , from adjacent blades 14 . this is because attachment assemblies 26 of hub 20 have , in effect , replaced the seventh and eighth blades . the two attachment assemblies 26 are at least partially visible in fig1 a spaced circumferentially about shaft 18 by approximately one hundred eighty degrees . symmetrical positioning of attachment assemblies 26 about shaft 18 presently is preferred , although situations may arise in which an odd number of assemblies 26 , or asymmetrical positioning of an even number of assemblies 26 , is desired . the exemplary attachment assembly 26 of fig1 a may comprise at least one recess 30 a . in the version of scrubber 10 depicted in fig1 a , recess 30 a is formed by a pair of spaced walls 34 a - b connected to hub 20 . a second recess 30 b , formed by a pair of spaced walls 38 a - b connected to hub 20 , also appears in fig1 a . shown especially in fig2 a - c is exemplary brush 42 . included as part of brush 42 is member 46 , which is sized and shaped to be frictionally fitted into recesses 30 a and 30 b . concurrently , clips 50 of brush 42 frictionally slide along walls 34 a - b and 38 a - b . manipulating brush 42 in this manner connects the brush 42 to scrubber 10 for use — as shown in fig3 - 5 . because brush 42 is likely to wear through use , it preferably may be detached from scrubber 42 ( as through manual force , for example ) for replacement . also included as parts of brush 42 are brush body 54 , fingers 58 , and bristles 62 . fingers 58 depend from body 54 , with each finger 58 comprising opposed major sides 66 a - b . bristles 52 protrude outward from these major sides 66 a - b . although fig2 a - 5 illustrate three fingers 58 depending from each body 54 , more or fewer fingers 58 may be present instead if appropriate or desired . fingers 58 beneficially are flexible . accordingly , as shown in fig4 , fingers 58 may flex as blades 14 rotate about shaft 18 . whereas major sides 66 a - b are nominally vertical when apc is upright ( e . g . fig5 ) and blades 14 are not rotating , flexing of fingers 58 causes major sides 66 a - b to become more closely parallel to the surface to be cleaned . consequently , because bristles 52 protrude outward from major sides 66 a - b , these bristles 52 become more closely perpendicular to the to - be - cleaned surface as the fingers 58 flex . bristles 52 thus in use may contact the to - be - cleaned surface so as to “ scrub ” the surface and suspend bottom - dwelling debris into the water of the pool for evacuation into inlet 21 of apc 22 . consistent with other suction - type apcs , apc 22 also may include body 70 through which the evacuated water may flow to outlet 74 and then into a hose , all under influence of a pump . moreover , because scrubber 10 rotates about an axis perpendicular to the to - be - cleaned surface , the speed of movement of brushes 42 ( and hence of bristles 52 ) relative to the surface may be faster than that of passive devices which merely are dragged along the surface . this relative speed of movement likewise may be faster than that of rollers , which typically rotate about axes parallel to the surface and in the same direction as the wheels or tracks of an associated cleaner . rotation of scrubber 10 about the perpendicular axis also requires approximately fifty percent less surface - area contact between brushes 42 and the pool surface to scrub an equivalent width of pool surface than would a roller , whose length must span that entire width . this decreased surface - area contact of brushes 42 produces less resistance on the drive system of apc 22 than would rollers , potentially enhancing the longevity and robustness of the drive system . if scrubber 10 is configured to rotate only in one direction , bristles 52 need necessarily be present only on whichever of major sides 66 a or 66 b is the “ leading ” side for purpose of the rotation ( as the other , “ trailing ” major side will flex away from the to - be - cleaned surface ). it nevertheless may be advantageous to include bristles 52 on the trailing major side 66 b or 66 a of brush 42 so that , when bristles 52 on the leading side wear , brush 42 may be switched to a circumferentially opposite location on scrubber 10 so that the previously - trailing side becomes the leading side and presents unworn bristles 52 to the to - be - cleaned surface . this switch effectively can double the useful life of a brush 42 . ( and of course , if scrubber 10 ever is configured to rotate both clockwise and counterclockwise , including bristles 52 on both major sides 66 a - b may be valuable .) the foregoing is provided for purposes of illustrating , explaining , and describing embodiments of the present invention . modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of the invention . also , although “ pool ” and “ spa ” are sometimes used separately , any reference to “ pool ” herein may include a spa , hot tub , or other vessel in which water is placed for swimming , bathing , therapy , or recreation . finally , incorporated herein in their entirety by this reference are the contents of the van der meijden application .