I have a newly built pool from a local builder. He can't seem to solve the issue in my spa. I've added a sketch and photo for reference. Water and air enter on the center as shown in the sketch and T off to 3 returns each with a 12" extension past the last return on each side (they are not connected in a loop). They are air/water mixing returns with eyeballs. On startup everything seemed fine but once the blower got turned on one return was not receiving water pressure, only air. This caused lots of water to spill over the side of the hot tub requiring me to add water to the pool after two uses. I've had someone (3rd party) come out and blow air from the spa return valve using a pressure plug and compressed air with all other returns plugged. There was initially no air coming through the return in the spa. We then reversed course and blew from the spa return back through the valve and got a great deal of water out. So we assumed there was a blockage, and blew back again through the valve and then received air into the spa from the water line. We put everything back together and the situation is the same. I've also attached the fitting that was used. I have a theory that the fitting used is defective, hole not cut out like the others or there is something with the hydraulics happening here. I'd like to get this solved and hopefully not have to bust out a spa wall to fix it.