I use to be a life guard and we swept everything to the main drain then turned on the main drain valve and sucked everything into the filter system. This was back in the 80s. I recently purchased a home in Houston with a swimming pool, my first. So I proceeded to clean my pool in a similar fashion. The dirt just piled up at the main drain. Nothing was moving. I checked my valves and everything was set. Still nothing. In fact, I almost drained the spa out. Apparently the spa drains are working. I tossed a plastic bag over the spa drains to keep it from draining, still nothing from the main drain. What the?
I tossed a cinder block into the deep end and dove into the pool. Holding onto the cinder block I managed to unscrew the main drain covers. Two of them. One drain simply had a lateral pipe connecting it to the other drain. First Faux drain. The other had a cap. A cap! What? Got some channel locks and took the cap off. Inside was clay, no pipe, just clay dirt. Maybe it was plugged? I got a long rod and poked the clay. I couldn't see a pipe down there. Two faux drains?
When I purchased the home there was one of those robot thingys cursing around. So is that the way we clean pools these days? Then why put those silly drains down there? I dunno. A friend told me he "thinks" they stopped using real drains for liability reasons. Something about kids with long hair getting hung up on the drain. Makes sense to me.
Let me know if anyone thinks that's what pool manufacturers do these days.