I changed it to 15, as well. I just had the mechanic look at it again. He thinks the only thing it can be is that the pump is bad. It shredded the brand new impeller that he just put in, so it spins but doesn’t prime. We filled up the bags with a hose and the pump will expel the water…prob due to the pressure. It won’t pick it back up from the lake. We tested the ball valve and it definitely let water in. We ran another pump to the front/center bags and it worked, which tells me that there aren’t any air holes in the lines. Has anyone ever heard of a pump that doesn’t work even if there’s a new impeller and the impeller spins???? It’s really the only thing left we can think of.