What are the best clamps?

What TSMB said. My big concern would be overtightening, the clamp here is just to keep the joint air tight and to keep it from falling off, which takes very little pressure. @Juanita - your description of a ‘two screw’ clamp makes me guess that the previous owner made do with two screw clamps from the hardware store, do they look something like two of these, connected end to end?