Why does dirty water comeback into the pool while you are vacuum have to waste?

There are a few reasons why dirty water might come back into the pool while you are vacuuming:

- You are vacuuming too quickly. If you vacuum too quickly, the suction from the vacuum cleaner will create too much turbulence in the water and cause debris to be stirred up again and sucked back into the pool.

- The vacuum cleaner head is not working properly. The vacuum cleaner head may not be creating enough suction, or it may have a leak that is allowing air to leak in and water to flow back into the pool. Try replacing the vacuum head or sealing an air leak if you don't think there is enough suction happening.

- Filter and skimmer baskets are too dirty, need emptying/replace cartridge: If water can't pass through the pump system with ease from these baskets being too full it has nowhere to go but out by where the vacuum hose has the pool water return going (return port).