Yah, I think Zag and Bull know more about this than I do. All I an offer is from my aquarium experience, so if BS's advice doesnt work, also check out your spaflex if that is what they are using. Make sure they used enough of the pvc cement (I prefer christies blue pvc glue) because if not enough glue is used, there could be a small enough hole where air can actualy get sucked in from, but not actually leak out. Its sort of a venturi. Happens alot in our aquarium systems, water is getting sucked in somewhere as Jeff said.
Good luck, and damn you for having too much fun down there
G