Main drain valve

Besides draining, what other times do you open the main drain? Do you usually just use the skimmers for your intake?

I'll be curious what experienced pool owners say with regards to your question. In our new pool, the valves are set to suck equally between the main drain and the skimmer. If it sucked only from the single skimmer I've got, it would suck both water and air, as the suctioning is strong enough to do that (even running my pump at 80% of max). I know that because the first time I backwashed my DE filter, I tried sucking from the skimmer alone (where I added the new DE), and was a little aghast to see the skimmer completely empty, and realizing that the flow into the skimmer basket wasn't fast enough to replenish the water being sucked out of the skimmer. So, it's half-n-half in my pool.

One thing I like about this is I hardly need to vacuum my pool. I've done so three times only since I got the pool (8 weeks ago). Whatever debris collects on the pool floor appears to, eventually, get sucked into the main drain, as my water is crystal clear.

The main drain has value other than draining out the pool. The water in the pool will mix better if you have it coming from the deep end as well as the pool surface. The chemicals will mix better, and probably since cold water sinks, it will also serve to better regulate your pool temps. I usually keep my valve in position to have the skimmers suctioning about 2/3 of the water, and the main drain about 1/3. If I shock my pool, which I do by broadcasting powder over the deep end, I'll turn the valve to the middle position to get more of the shock into circulation. If I have alot of garbage floating on the pool surface, I'll set the valve to only the skimmers for a few hours. But my usual every day setting is 2/3 skimmer, 1/3 main drain. Hope this helps.

Tom