Cavitation, Mike.
something is creating too much suction drag upstream the air trap.

1. Connect your air trap to a simple jug with a large bore tube. If the air trap still sucks in, its filter is the culprit.
2. If the air trap does not suck in any more, then your tanks have a problem. Could be coming from the clunk lines or the fuel stopper. In that case, you could try one tank after the other to see how much restriction you get with only one connected.

Please report here with pictures and we'll try to help you.