Back when I was in grad school and only had a utility closet to use as a darkroom, with no running water, I made a sort of vertical processor with 3 or 4 slots each for dev/stop/fixer, out of acrylic. This is a bit like making a vertical washer, smaller, but with a greater requirement for keeping the solutions separate. In a washer, you just need dividers, not individually sealed compartments. I used precut 12x12" sheets of acrylic from a plastics store on Canal St in NYC, and acrylic strips for the edges between the sheets. It worked, but leaked a little, so I had to stand it in a tray to avoid a mess.
A few thoughts:
- The solvent usually used to glue acrylic contains methylene chloride and is extremely nasty (toxic/carcinogenic). Use this outside if you must use it. Someone upthread was able to use RTV, which is more innocuous. Research what glues will work with the plastics you plan to use.
- Even my small acrylic processor wound up quite heavy. Plus filling a big tank with water is super heavy. Of course, if you use an aquarium as the outer tank, it's designed to take the water weight, but make sure you have a plan for where you are going to put it and a fill and dump routine.
- If you use RC paper, it washes quickly and you don't need an elaborate washer.