Abstract: A main drain of a swimming pool has a housing, a removable cover, and one elongated opening formed therein. In one embodiment, the housing is oval in shape with the elongated opening running parallel to the major dimension of the housing to provide a single extended opening that would be difficult for a swimmer to obstruct. In an alternative embodiment, the elongated opening extends over a round cover and is H-shaped. Each elongated opening is formed to have an internally curved flange to provide a smooth edge and structural stiffness for the cover. The single extended opening with its smooth, rounded edges reduces the likelihood of entrapment and entanglement and allows large debris, such as leaves, to pass more easily into the main drain.

Abstract: A canister filter for use with a swimming pool water circulation and filtration system includes a lower manifold with two pump fittings so that two pumps may be connected to one filtration canister. The canister also has an upper manifold with two fittings for connections to different main drains, an equilizer port fitting, and a relief port fitting. The canister housing may optionally contain a venturi tube that can be used to augment the suction of a single pump to allow the elimination of a second pump, or, alternatively, allow additional main drains to be added to the pool without increasing the number of pumps. The single canister filter can thus be used with two pumps and drains or two sets of drains, while providing relief in the event the drains are blocked.