Originally Posted by EricW
Ahh very good idea. It has predrilled holes, I'm betting I would need to add a new hole? Otherwise getting the tube in and threaded to the fitting might not work?
Normally those holes are already threaded. Most of the tanks you buy from surplus dealers on ebay come from a manufacturer that designed them for plumbing.
If you needed an extra hole, say for venting, id take a hole saw just smaller than a pressure relief valve, and manually screw that puppy in. That way you just flip the little lever and it's open, flip it back and it's closed.
The inside tube could be flexible plastic hose, or even pex tubing crimped on to adapt to a rigid plumbing fitting.