John, there was a thread a while back showing how to make paper filter clunks out of a cartridge type filter, as opposed to the type you're thinking of. It basically duplicates the filter clunk found in chain saws, so I'd go to a small engine repair shop first and take the tank along for sizing.

I would give SERIOUS consideration to an air trap though, regardless of clunk type. Very effective and cheap insurance for your multi-thousand dollar investment.