You could even use something hot to melt those edges a bit so they arent sharp - they might well pop the tubing right off.

I think it would work fine other than the fact that an empty 2L bottle would be so light it would wobble and roll when they were trying to get into it. I'm sure theres a way you could get around that though.

It's certainly cheaper than buying dollar store tupperware and melting a hole in it (though the removable lid for cleaning out that sphagnum sho is nice).