Rub-a-Dub-dub, I clean in a trough (sorry, very bad rhyme..)
I have cleaned in a hottub, stirring with an oar. Really low-tech, but works.
My present system consists of a 2x6 framework that is 16 feet by 4 feet. The framework is bolted together so that the bolt heads are on the outside, away from the sail. I line the framework with a large plastic sheet and fill with water. You need to find a flat surface in order to keep a reasonable water depth.
I pull the sail into the trough, one section at a time and brush with a soft bristle brush. Flip the sail and do the other side. I use a half cup of liquid dish soap. Wear water shoes so you can walk on the sail and in the trough.
Then I hoist the sail to the top of my garage, rinse with a hose and stretch it out to dry. I have also laid it on my lawn to dry. Both methods work fine. The lawn dry is easier.