Honestly, I really don't know if turning the tank upside down creates big problems. Never tried it.
None of the regular homebrew tanks have a siphon tube. It needs to be installed specifically, and on an empty tank.
But the larger question remains: Why do you lose gas? I would trace and fix that, before anything else, regardless of whatever tank you've connected.
Leaky regulator? Leaky connections? Bad O-rings? Damaged Sanke coupler?