Abstract: A trap for grease or other foreign matter dissolved or entrained in a liquid comprises a housing containing a chamber for receiving the liquid to be treated, a turbulence reducing channel for conducting the liquid from the chamber to a settling tank, a cage for trapping trash as the liquid enters the tank, a grease collector at the normal surface level of the liquid in the tank, a trap for collecting sediment at the base of the tank and an outlet for draining decontaminated liquid from the tank. The outlet may be in communication with a liquid seal and means may be provided to syphon the liquid from the settling tank. Means may also be provided to cool the liquid in the housing. The housing is in modular form which is preferably segmental in plan. An assembly of such modules may be constructed with a common outlet in the shape of an all but complete circle or polygon. In this way access may easily be gained to the trap for servicing, maintenance and repairs.