A sump pumpA sump pump is a device used to remove water that has accumulated in a sump basin. Typically found in the lowest part of a basement or crawl space. Its main purpose is to help keep these areas dry and prevent flooding or water damage. More is a device used to remove water that has accumulated in a sump basin. Typically found in the lowest part of a basement or crawl space. Its main purpose is to help keep these areas dry and prevent flooding or water damage.