So what does a sump pump actually do?

A sump pump will be found inside the crock pit installed beneath the basement floor.  The crock pit (if you have a pressure relief system) will be where the water under your home is collected. When the water reaches a certain level inside of the crock pit the sump pump ejects the water outside of your home.  The specific pump that we use Zoeller 1/2 HP  can eject up to 4300 GPH (Gallons Per Hour).

Read more here:

-Installing waterproof paint on foundation walls vs a pressure relief system (sump pump system)