my tube is plastic 2x9 and I bought it at a pet store, in the aquarium section. it works fine, about $12. I did have to put a thick rubber pipe coupler, $3, to soften the edge. it works fine, I pressure it up, and it does start to flex in, but that is a lot of pressure. I actually need more diameter. I am over 6" in girth, and when hard I fill it completely girth wise. I am looking for length. I am 7.25" long and would like to get to 8" at least.
my vacumm pump is an automotive brake bleeder pump I got for $24. so I got about $40 invested in a pump that works pretty good.