sorry haven't gotten that far... but I am told you need to make yourself a little splash gaurd to keep the solution from geting sloshed up on the walls, cabinets and such... i'm sure somone here would be able to tell you how to build it for not much $$$
You can make yourself a splash guard from a piece of the black stiff plastic that is sold at home supply stores and garden centers to separate between planted areas and lawn areas or walkways. Glue or otherwise connect it into a circle just large enough to fit on the floor surrounding the Challenger's pad driver and tile/grout brush. Then scrub away and this ring will contain the dirty liquid. The most readily available stone & grout cleaner is the Tile Lab line, sold in the vicinity of floor tile products at any Home Depot.