OK, so problem solved. The drain king did the trick. I put it down the hole via the skimmer port as far as the garden hose would go with the 10" drain king attachement, turned on the water and blammo - bubbles and crud came up through the pool drain cover.

Unfortunately, I also wasted $30 on a KleerDrain gizmo at Home Depot that was supposed to fire a CO2 cartridge down the drain. It probably just did not fit tight enough into the pipe opening, but this gizmo did nothing. The $10 Drain King was an immediate fix and far cheaper.