The federal VGB Act allows the use a single unblockable drain, as an alternative to multiple smaller drains.

Some state codes, however, still require multiple drains in all pools.

What is “sump depth” and why does it matter since it is under a certified drain cover anyway?

The word “sump” refers to the space between any cover and the suction piping supplying water to the pump.

As water passes through the cover, headed for the suction pipe opening, turbulence is created and when strong enough it will tangle and twist hair.

This has the potential to lock it in and around the drain cover.

Turbulence, and suction power, become more extreme as the flow increases and at some point, ALL drain covers will tangle hair. This is one reason why drain covers have a flow rating that must never be exceeded.

The the drain cover is missing, is it okay to swim if the pump is turned off?

NO!

The open pipe creates a

DANGEROUS risk of limb entrapment.

An arm or leg can get stuck in the pipe. This has happened, especially with children.