Does my pool have an overflow drain?
Moreover, what keeps a pool from overflowing?
Some pools have a hose spigot plumbed after the pump, or on the filter valve, which you can connect a garden hose, to lower water level. Or, you can use a submersible pump, aka pool cover pump, to keep the pool from overflowing. Finally, there is the siphon method. A pool vacuum hose works best.
Accordingly, how does a pool overflow system work?
It's alonside your pool so the water level in both is the same. The water gets too high and it starts to run down the big pipe down to the drain. If you want more control, you can do some plumbing modifications.
Swimming pool builders often install overflow drains near the rim of the pool that prevent flooding most of the time. If you don't have an overflow drain, or if it is clogged, it is possible for periods of unusually heavy rain to overflow your pool.