I am ignorant! e.g.: Do I even have real main drains

I have had a small IG Gunnite pool for almost a year now, with NO problems at all. In fact, this new pool is frankly as clean as any I have seen, and my maintenance is minimal (which is the ignorant thing I am getting to...)

Brief Background: Sta Rite pump and cartridge filter. It has a frog system that keeps low level chlorine and ph in check. I rarely add additional chlorine (other than the frog bac pacs, and even those are not that frequent), and if i do add it, it is cheap bleach. I brush frequently, and the kreepy krauly picks up literally any debris it comes across (although it seems to already be wearing out - I may be over running it). There is not a lot of vegitation around, which helps it stay clean. The builder put an ozonator in there, which produces a neon light and some bubbles and probably little else .........

Anyway, my two questions:
This little pool has one skimmer, that usually has the kreepy in it while operating. Even still, it pulls a lot of suction, and skims through two little holes in the kreep krauly skimmer cover while also vacuuming. (Two holes are covered, two are open) Often times, especially with still water, it creates a vortex and chirps out a loud suction sound intermittently. Is there a device that can minimize this? I might need a higher water level, but it seems ok frankly. Is there a way to throttle back the pump suction a bit?

Second, and related, I have never run suction from the (two???) main drains, because I have never had a need to. But it occurred to me, if I did want to create suction from the drain ... I would not know how. Could I just plug the skimmer hole? There is only one 'valve' on all my plumbing, and it clearly has nothing to do with drain suction, because it is located after the pump and filter, and frankly i am not sure what it does either. It basically is a jandy valve that is located at a Y coming out of the filter. One branch of the Y seems to go right to the pool, and the other goes through the frog, and then right to the pool rejoining the other branch!

Yikes, that was long winded. Any thoughts?

Your skimmer should have come with a flying-saucer-looking device called a float valve. It sits in the bottom of the skimmer, covering the two holes creating a suction at the bottom drain port. If you want the bottom drain to work, you need to adjust the small teardrop-shaped flap to cover about half the hole in the bottom of the float-valve. If there is a hose connector in the suction port of the skimmer it will have to be removed for the device to fit properly.