In our part of the country with a water table that doesn't typically cause any issues because it is so deep we don't use hydrostatic relief valves.  Instead we plug the port in the bottom of the main drains as the pool is being filled.    The other hydrostatic relief plugs not in the main drains (closer to the shallow end) also get plugged.

When the customer every has to empty their pool, we advise removing the plugs just to be on the safe side (even though our water tables are very very deep (40+ feet.)

My question is...does anybody else use plugs like this, and if so, do you put a piece of perforated pipe below the main drain where the plug is or do you rely on the stone base to allow for water flow?

tony c