Hah. That's what I was on here searching for: how to find fittings that will work??? I'm trying to run my CO2 into the filter return thingie. Seems like Fluval uses odd size tubing. Makes me crazy, cuz I wanted to hook it up right now!I have hooked CO2 up to output of canister filter before. The pain was finding hose fittings to hook up the air tube without water leaks. Hooking up to shower pipe is probably easier.