I can't get my main drain to prime

Every since I had the pool opened a couple weeks ago, the main drain wont prime. I know it works because I purchased the house near the end of summer last year and it was running fine. The previous owners had a pool company service the pool, so when I purchased the house I called the pool company that was servicing it to see what they would charge per month to continue taking care of the pool for the last 2 months of summer. After talking to them, I decided to just try it myself with it being my first pool (which was a bad idea..must have went green 3 or 4 times, LOL) for the rest of the summer but one thing he did mention was that it was really hard to get the pumps to prime if it was off for a while. I never noticed it the rest of the summer since I ran it 24 hours a day....and never left it off long enough except to backwash for a few minutes.

The end of summer came, and I had a different company install a loop-loc and close the pool and then when summer came this year they came back out and opened the pool but they were unsuccessful in getting the main drain to prime so they left it off.

I can leave the skimmer valve turned on but as soon as I open the main drain everything loses its prime and stops working.

Any secret to getting this to prime?

Picture of set up. Main drain valve furthest to the left which is currently in the closed position. Everything else in the open position.

https://lh5.googleusercontent.com/-w...0/a25dc236.jpg

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.

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

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!