44 on each sidewall 21 near the middle thereof fig2 housing walls 21 23 and 25 terminate in a bottom lip 20a which seats over the top edges of buckets 72 and 82 a central inverted sealing channel extends between sidewalls 21 near the center thereof and seats over the top edges of the facing flat vertical walls 75 of buckets 72 and 82 carriage 50 has an upper portion 52 and a lower portion 54 fig4 and 5 each of molded plastic the upper and lower portions 52 and 54 snap together to capture a rub strip 56 that circumscribes the perimeter of carriage 50 upper portion 52 of carriage 50 has an elongated toroidal shape with a downwardly projecting inner wall 58 lower portion 54 is of mating configuration and includes an inwardly projecting bottom rim 60 and a crosspiece 62 extending across the middle of lower portion 54 to define a partial floor for supporting buckets 72 and 82 rim 60 projects inwardly beyond wall 58 such that wall 58 rim 60 and crosspiece 62 define an elongated oval shaped bucket receiving well 68 fig3 crosspiece 62 has a stiffening contour 64 in the preferred embodiment carriage 50 also features casters 66 mounted in the bottom of lower portion 54 buckets 72 and 82 are removably held in receiving well 68 of carriage 50 in the preferred embodiment buckets 72 and 82 each have vertical sidewalls 71 flat bottom 73 a flat wall side 75 a hand grip 78 and handle rests 80 fig4 and 5 buckets 72 and 82 are generally 34 d 34 shaped in horizontal cross section such that the flat sidewalls 75 can be.