By the time he left, the pump was working fine and not a drop of water was leaking from the temporary plumbing he hooked up.
Seven hours later I had the water pumped out as much as necessary to see the leaks. There were several dozen water spouts coming out the wall.... the same area that has always been the problem area. About the only way to locate those pinhole leaks is to fill the tank and then drain it rapidly. It's been about six years since we've done that so I guess I can't complain too much.
So much water got trapped behind the tank wall that it eroded a patch of the wall (about 2 sq ft area). I didn't see water coming from it into the tank, so am pretty certain that was an effect of the leakage, not the cause.
Tomorrow will be another grueling day. I need to mix cement and bonder and fill every single leak (I marked them with chalk), then coat them with tar and/or water sealer until I run out of it. Then Friday I'll refill the tank. That's the plan anyway. You know what they say about plans. 'Life is what happens while you're making plans.' At any rate, once I get done and refill the tank, however much or little it leaks is going to be how it is. I'll live with it. Hopefully, I'll still have enough water to fill it.
Didn't get time to look for birds today. I had to keep the pump serviced and wade in the tank to locate and mark the leaks. Any birds I saw were by accident. That darn sapsucker is now ravaging an ash tree since I've barred it from the locust tree. I'll sure be glad when he leaves.
I can't understand why the mesquite tree near the tank's leaks isn't growing huge. It would sure mitigate the loss of the water if it was. (On the first photo it's peeking out at the right side.) Maybe mesquites are just slow growers and last year the tank had zero water in it, therefore, no leakage. And, of course, I've never watered the tree. But I'd think it would be showing lots of new growth this summer. It's not.