You will need 12" of 1-1/2" ID pipe, 3 - 1-1/2" ABS couplings, 2 - 1-1/2" ABS end caps, small container ABS glue, 4x4" sheet of rubber roughly 1/8" thick, a razor blade and a hacksaw.
Cut 1 piece of pipe 6", cut 3 pieces of pipe 1" as square across the ends as possible. Cut 1" pieces first, it's easier.
Cut 3 pieces rubber the same size as the outside diameter of the pipe. Use pipe to draw a circle. TRIM CAREFULLY so the pieces of rubber fit inside the couplings comfortably (not loose).
After all three rubber pieces fit well, cut each piece as shown above to allow liquid to flow through tube. DO NOT BE AGRESSIVE. Once all the pieces are made, assemble tube (do not glue yet) and pour water through. Be sure to assemble with the rubber pieces 180 degrees to each other to allow water to flow into tube but keep light out. You should be able to pour the water through without having to stop pouring. If the openings need enlarged, disassemble and cut more off the rubber pieces being careful NOT TO TAKE OFF TOO MUCH AND ALLOW LIGHT TO ENTER THE TUBE. Check to see if light enters tube by looking through the tube while pointing it at a light source.
Glue pieces together once you are satisfied with how the water flows in and out of tube and there is no light leak. (Do not glue ends caps on: sorry)
After the tube is glued together, if the end caps do not come off easily, lightly sand the inner surface with a fine grit sand paper until they do making sure you clean them thoroughly before using. The only reason for the end cap on the end where you pour in chemicals is to keep chemicals from coming out while you roll back and forth while developing. You could drill a hole (3/4"?) dead center in this cap and prevent this problem.
I do not know how much chemicals it takes to process film or paper in this tube. You will have to experiment 2" pipe will do 5x7's. 3" pipe will do 8x10's. 4" pipe will do 11x14's.
Expect to pay more than $5 for the larger sizes.
e-mail questions to,email@example.com, not the group if you have questions. Good luck.