Main Drains are installed in the bottom of most in-ground swimming pools. They perform a function similar to a skimmer in that they allow water to go from the pool to the filter system to be cleaned. Main drains do not have baskets to trap debris from getting to the pump and filter so keeping your pool clean and clear of debris will allow the system to run well and help circulate the chemicals.

The main drains are usually located on the lowest point in the pool, so the entire pool surface slants toward them. Most of the dirt and debris that sinks exits the pool through these drains. To keep people from getting their hair or limbs caught in the plumbing, the drains are almost always covered with grates or antivortex covers (a cover that diverts the flow of water to prevent a dangerous vortex from forming).

What does it look like, you ask? Well, t looks like a large white (or black, for dark marbledusted pools) circle or rectangular grate on the bottom of the pool, in the deep end. If you see multiple circles or grates at the bottom of the pool, you may also have hydrostatic valves, which keep the water pressure inside and outside of the pool equal, in high water-table areas.