On modern steel hulled ships, a sea chest is located below the waterline and usually along the bottom of the hull. Leading away from the sea chest into the inner-bottom of the the ship, it will connect to the specific systems piping. Sea chests can be designed to accommodate either suction, discharge or both.
Most sea chests will have some form of grate or louver at their openings to prevent the uptake of foreign matter. For example, the cooling water system aboard a ship will begin with a sea-chest uptake at the lowest part of the hull, then lead upward into the cooling water piping with suction being provided by a pump. After circulating through a heat exchanger to provide cooling water to the engine, the now heated water will be discharged through another pump, into piping leading away from the pump and down through the ship and finally discharged to sea through another sea chest.
The use of sea chests allows for repairs of exfoliated steel in and around the highest wear areas and protects the more critical (and expensive) copper-mickel piping systems.