When I had a HOT, I simply used a piece of medium grade pond filter media and cut a small piece to sit into the return ramp, thus trapping any excess bubbles before they could fall back into the tank. This was when I ran a @#@#ed up Sea@#@#@.
If your HOT has a return line rather than a ramp, you could always rig up an overflow/riser cup underneath the return, thus allowing the air bubbles to rise to the surface along with the water so that would help the bubbles escape at the surface.
cheers, sumpfinfishe
