I can't get my main drain to prime

[Zac851]

Well, I finally got it going yesterday..sort of. Every 5 minutes or so, I would turned it a 8th of an inch or less until it was finally all the way open but I've got a bad leak somewhere. Its blowing bubbles out the returns for a second and then water and just doing this back and forth. I dont see any visible leaks anywhere.

[PoolDoc]

Finding suction leaks is a pain; I never bother till they are causing a real problem.

Places to start:
+ pump basket lid & gasket
+ pump suction inlet
+ valve bodies and stems
+ unions

[Anonymous [GDPR] European in Spain]

If the skimmers do not loose their prime it is unlikely to be related to the (but still worth checking)
a) pump basket lid & gasket
b) the pump suction inlet.

Have you ever had enough debris in the bottom of the pool to clog the mesh grill on the main drain? I once had a plastic pipe collapse at a glued fitting when by mistake a valve was closed on the suction side.

I would start by removing the suction manifold at the valves and pump and making sure all the "O" rings are in good order on the valve stem and the valve body to manifold joint, if they are then I would be looking at making up a fitting to back flush the main drain line, just in case there is a blockage and before you start digging things up.
Best of Luck!