mas985 wrote:A pool bottom is much flatter than a toilet bottom which is more funnel shaped so "debris" is more inclined to move toward the toilet hole than the main drain. The toilet has a fairly large hole for "debris" to pass while a pool main drain has many very tiny holes which only fine dirt can pass through. A toilet uses gravity to flush while a pool use a pump to create water flow. A toilet flushing looks nothing like a main drain running (i.e. no swirling action). The physics are substantially different between the two and the toilet is going to be much more effective at removing debris than a main drain.
Also, I don't disagree that a main drain can have decent flow rate but it is usually a little less than a skimmer because the pipe lengths are longer. But even it was the same, the flow rate doesn't do much in the way of debris removal. If you don't believe me, dump a small amount of dirt directly around the main drain and see how much dirt it actually collects (without the help of a cleaner or vacuum). You will be very surprised at how little is removed.
But you are so predictable!
I wrote this piece specifically for you. And you jumped right on it.
The suction in any pool return branch is related to distance from the pump and of course the depth in the case of the main drain. My main drain is half the distance of the skimmer I use.
(The second skimmer I do not use, because filtering clean water that is spitted by inlet to the surface right next to it, I consider a waste of electricity as well as unnecessary prolonging the cycle).
Also, you completely forgot about the selector valve.
I built my first pool in 1974, so please do not patronize me with your suggestions to "watch action of the main drain". I have installed the new safety cover 2 years ago, with the new plaster and it sucks in parts of oleander leaves and the flower stems as well!
Now to the point:
With the selector valve aimed on main drain only you can actually clean fine sand dust (settled in your pool after the sand storm), just gently using the wide brush toward the main cover. You see I have done it and not just once!
It may take an hour or two, but it would take a regular pump 8-10 hours, with the pool sweep activation 10-16 hours and in the same pool without a main drain at least 3 days!!
I sincerely admire your willingness to make a spectacle of yourself here in such a clear cut argument.
Maybe you have your original opinion about the "global warming" supported by a video as well.