This is my test piston I made for a 1" schedule 40 PVC pipe. I cut and spliced (2) 3/16" O rings (cut length 70mm) for this, and it threads onto 1/4-20 threaded rod. I tested this, putting it in a pipe with about 10" of water over it and left it for about 24 hours, no leakage, so I'm decently pleased with it so far. With a little oil, it takes about 2 pounds to move the piston. I hope this could take shop air (120 psi), I think it could. See http://www.thingiverse.com/thing:717976 for O Ring Splice Jig See my blog entry at http://ryanfabrications.blogspot.com/2015/03/piston-test-print.html Print, Make sure it fits in your PVC pipe, Tap hole with 1/4-20 threading tap, (optional) Coat with polyurethane or very diluted PlastiDip, Affix O Rings, Attach to rod, and Done