I'm interested in partially draining my pool a few times because CYA is off the charts. Being new to all this, I thought I could just use my regular pool pump to drop the level a few feet, then refill it. This is an in ground pebble tec pool. When the water level got to the skimmer level, I quickly realized that I don't understand how the plumbing works, maybe someone can help me out. The pool has two drains, one skimmer and a suction port we use for a crawler. The skimmer bottom has two holes in it, and it has a device in it with a little "door" to adjust skimmer flow, and a float that drops down when the water level is low, presumably to prevent the pump sucking air through the skimmer. At the pump there is a valve that chooses between skimmer/drain and suction port, which I use to tune the suction to the crawler.
I thought that the device in the skimmer would allow the water level to go below the skimmer while the pump continued to draw water from the drains. This is partially true but what I observe is that the pump sucks against the blocker in the skimmer for a minute or less, then the skimmer fills up partially with water and the thing floats up. This confuses me. What are the two holes for in the skimmer? Is the drain connected to the pump via the skimmer (one hole is from the drain, the other to the pump)? If so, why?