Main Drain clog

[Azsnook]

It was powdered CYA and I put about 2 to 3 pounds in the skimmer. A significant amount settled in the conduit that runs from the skimmer to the main drain. Prior to this, I could set my pump to main drain without cavitation, now my pressure drops to near zero with severe cavitation if I valve it 100% to main drain. As far as capping my vacuum port, I was considering pressing a tennis ball in the port to force the water to travel to the main drain plumbing. Any thoughts?

[PoolDoc]

I once stopped up a line like that. So, I took some 1/4" tubing, and hooked up to the pressure side and then snaked it down till it reached the clog. It took a couple of weeks, but I eventually dissolved the clog.