O-rings?

[Ol'fogasaurus]

http://www.instructables.com/id/Homemad ... nd-tubing/

Not sure about this as being an always but for what it is worth.'

Lee

[Piledriver]

Note that it will ALWAYS be far, far cheaper to buy a prefabricated oring from an industrial seal place---
Some have minimum orders, I got a free set of viton orings for a Type 4 once as it came to like $5 for 16 viton orings and it wasn't worth the paperwork...
I bought in bulk after that, was not a whole lot more than the $25 minimum for 100 of both sizes.

For odd//huge sizes, the rubber silicone, buna-N, viton at least are available in rolls to be glued together as well. (in all std diameters)

Super glue and a sharp single edge razor blade are the tools of choice, cut at a shallow angle for max area
(both ends at the same time to match the angle, watch for an ugly twist, keep the seams aligned for best results)

I'll give they guy an A+ credit for trying, and it might be a good method in a pinch.