Instead of using knots could you use a Solomon Bar or whipping to hold the PVC in place?
Just to make sure I'm understanding. The loop is larks headed to the rings, passes through the PVC, channel, PVC and is again larks headed to the rings?
Also I haven't done much with PVC pipe. So, does it go pipe with hole, connector, short piece, connector and second piece with hole? I'm guessing they're not glued?