OK, so I took one of the black loclines off, which left a threaded end. I had a piece of tubing that just fit over that threaded end. I put the tubing on and adjusted it so that all the air was out of it. Still bubbles. So I opened the valve wide open. The bubbles decreased slightly, but they're still there. I held a flashlight up to the clear tubing leading from the pump. I saw bubbles there with the old sump, but I don't see bubbles there now. That tube tees off to the clear tubes that lead back up into the overflow boxes. No bubbles in those tube, and neither is leaking at the connection to the tee or to the overflow boxes. That leaves only the pipes that come from the bottom of the overflow boxes up to the locklines. Most of that is underwater, except for at the top of the pipes there are 3/4" 90s, 3/4" threaded couplings, and the loclines. I removed the locline on the right, so the only possible place for air to be entering is the 2 sides of the 3/4" 90. Right?