The number of connections shouldn't determine wether you have an air-tight system. Good thing cars or space shuttles aren't designed like that! Sucking air in is hard on the pump impeller (cavitation) and should be avoided at all costs.

OP: check your jandy valves on the suction side. Usually the o-rings in there harden and go bad after several years. You can use a 2' - 3' length of 1/2" PVC pipe as a stethoscope to listen for bubbles. Put one end to the pipe after the valve and one end to your ear. If you hear gurgling, you've found the culprit. If not, move on to another. If you don't hear any gurgles on the suction side, the air leak may be where the suction pipe joins the pump strainer, or the pump lid may be leaking. If it is an o-ring or pump basket cover seal leaking, replace the o-ring and be sure and use silicone lubricant when you put it back together, that'll ensure a leak-free seal. Also be sure not to pinch the o-ring when putting the jandy back together, that's easy to do with the big o-ring for the body.

Michael