Thanks for the replies. Smaller tubs just don't work well and 48" kiddie pools are too big. The current need is OBE - I was able to jam a freewheel removal tool (of sorts) onto the freewheel and break it loose. Strangely enough the freewheel wasn't tight. That allowed me to discard the rusty offending 1/2 pound dork disk.
I've decided to build a 28" square wood frame approx 8" high. I'll lay that on the concrete floor and line it with thick plastic sheeting. I think that's the best size to minimize the amount of solution and keep costs down.