Chris:(posted 8098 days ago)Acrylic plastics (Plexiglass, Acrylite, etc) are totally inactive to working strength black & white chemistry. I have been making my own tanks, trays, and washers out of the stuff for well over 20 years. My 220 roll film tanks have probably processed over 1000 rolls by now, never once have I had a problem with either the film or the tanks.
One caution: full strength acetic acid will react with acrylics, so make sure you mix your stop bath in a separate container. Also; don't leave water in them for looooong periods of time (several weeks), as the joints may degrade a bit.
Acrylics are good plastics for this sort of thing, but don't underestimate the weight of the liquids in a 20x24 unit.... the sides may be prone to bulge out. I suspect that 1/2 inch thick sides will bulge unless reinforced with extra bracing. I made a 12-slot 16x20 washer that holds about 20 gallons (167 lbs, plus the washer itself), and I had to reinforce the 1/2" sides. 1/4" dividers will probaly survive bulging.... if you fill them simultaneously. Have fun.