Rainman: Thanks for the reply...that might be doable, and I may even have some logs soon. I had some ideas about using lumber in some way, but not tree trunks...I like it.
Snrub: Thanks for replying again. I had been trying to think of some way of incorporating a large culvert pipe, but had not thought about the welding cap/nipple/valve part...good idea. I agree with you on the drawback of the valves. If you were going to do something like that would you encapsulate it in concrete to secure it for post-construction from a blowout given its such a relatively small area?
