All fixtures with a potential to carry grease-bearing waste shall be plumbed to the grease trap.
The first step in determining the appropriate size of the grease trap is to calculate the total number of fixture units connected to the trap. The following fixture unit counts shall be assigned to each different kind of fixture:
Kind of Fixture
Trap and Trap Arm Size
3 compartment sink
2 compartment sink
2", 3", 4"
2, 3, 4
Floor Drains (2", 3", 4")
2", 3", 4"
2, 3, 4
Floor sinks (3", 4")
Notes: Hand sinks are not required to be plumbed to the grease trap. For indirect waste systems where hub drains and floor sinks are used as receptors for dishwashers, 2- and 3-compartment sinks, etc., the fixture unit count shall be twice (2x) the floor sink or hub drain fixture unit count. In such cases the fixture count for the indirect waste source is not counted. As of January 2008, garbage grinders and disposals are prohibited in commercial kitchens and other industrial users of the sanitary sewer system. The next step is to determine the minimum flow rating of the grease trap. This is done by multiplying the total fixture unit count times three gallons/minute:
Grease trap flow rating = Total fixture unit count x 3 gallons/minute
The minimum liquid holding capacity of the trap is calculated by multiplying the grease trap flow rating (in gallons per minutes) times twelve minutes:
Facilities using dishwashers or wok stoves are required to install 2-compartment Traps with a 12-minute total retention time. Facilities with limited kitchen fixtures such as a pot sink and 1 or 2 floor drains may be exempt from the 12-minute retention time after review by Pretreatment Program personnel.
Upon approval from the Pretreatment Program, fixtures receiving non-grease-bearing wastes may be drained through a grease trap, but shall not be included for grease trap sizing (i.e., condensate from coolers).
The Pretreatment Program shall apply these grease trap sizing criteria in combination with its best professional judgment as a part of the approval process. In many cases this may mean that a larger grease trap may be required than the one specified by the sizing criteria. Under certain circumstances, a smaller grease trap may be approved. However, in no case will a grease trap with a liquid holding capacity of less than 100 gallons be approved for installation.