Finding the right "contraption" to effectively push air in to the returns lines has brought me to this point. While I know that using the a 6hp shop vac is putting a good amount of air in to my bottom drain, I'm not getting any bubbles from the main drain, even after multiple minutes. Has anyone tried a drain bladder but using compressed air vs. water to "inflate" the bladder and push air in to the main drain line? Example of a drain bladder for those who haven't used/seen them before: . Already own a drain bladder and its a perfect fit for the opening from the return lines running in to the pump basket.

I already own an air compressor. Purchased a "compressor-to-garden hose" fitting on Amazon today (same day delivery, nice!) Plan on bringing my air compressor tank to a high volume and then _slowly_ releasing the air (via a regulator) until the bladder inflates. At that point, I will have a seal on the line going in to the pump basket and air will begin filling the main drain [of course with the multi-value in the right direction]. No need to go much higher in pressure than inflating the bladder because all air at the point will be directed to the main drain. Let it run for a few minutes while pushing water and air out of main drain. Turn off compressor while simultaneously turning multi-valve and locking air in pipe.

Thoughts? Am I completely missing something?

Thank you in advance. Will post results after testing.