Based on that reply, I'm not sure it's really an issue. I do know the sight glass was full before we lost prime due to the suction cleaner sucking in air when the level dropped to low. However, since the pump is maintaining prime now and the filter is within operating pressure (15PSI of a 10-20PSI rating), and the water does appear to be clarifying, perhaps it's a non-issue?

I hesitate to modify the system where this place is a rental. If I was to add an air bleeder, where would I do so? The only 1/4 NPT fitting on the filter that I see is the pressure gauge.