Just wanted to thank you all for the recommendations. I completed making the developing tubes during the week and just got done developing my first LF negative using the tubes. I forgot to order Pyrocatechin in time and so developed this negative in FX-39 just as a "proof of concept" and it worked, no scratches from inserting/removing the negative from the tube, no light leaks from the end caps (I had to use Schedule 40 - white plumbing end caps and had to cover it with duct tape.), no fluid leaks, easy to use.
If anybody wants information about the pipes, just ask. Each tube (the part into which the film is inserted and the part which gets the developer) are of equal size. Each tube takes 120ml of developer.