No, you don’t. Personally, I like to skip the main drain because they do nothing for cleaning and/or circulation that can’t be done by other things.
Do You Need A Main Drain in A Swimming Pool?
We use a lower return or an even return pointed downwards for better circulation than the main drain and it works wonders.
The main drains these days are created to keep the water velocity as low possible so that they can draw water from near the drain and above it but that is just about it. Whereas a return can have very high exit velocity and affect the entire pool.
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As for cleaning, we use an automatic cleaner that does a far much better job of cleaning than a main drain. Again, because of the low entrance velocity, this is unable to attract bottom dirt beyond a couple of inches of the drain.
Another reason we don’t advise a main drain is in the case of plumbing issue. They’re harder to fix than a side return or skimmer plumbing which can be reached with a little digging.