(1) Grease interceptor compartments. Grease interceptor tanks must be designed and constructed with a minimum of two compartments. This standard may be met by one tank with two compartments or by two single compartment tanks in series.

(a) The capacity of the first compartment must accommodate at least one half but no more than two thirds the total required liquid volume; and

(b) The capacity of the second compartment must accommodate the remaining total required liquid volume.

(2) Grease interceptor inlets. Grease interceptors must have inlets that meet the following:

(a) The sanitary tee or baffle must extend into the liquid a distance within eighteen inches from the bottom of the tank;

(b) The sanitary tee or baffle must extend above the liquid surface at least to the crown of the inlet pipe; and

(c) The invert of the inlet pipe must be a minimum of two inches above the invert of the tank outlet.

(3) Grease interceptor outlets. Grease interceptors must have outlets that provide for adequate grease storage and the outlet sanitary tee or baffle must extend:

(a) Into the liquid to a point between six inches and twelve inches from the bottom of the tank; and

(b) Above the liquid level sufficiently to allow scum storage and venting, and to a point not less than one inch from the underside of the top of the tank. The outlet tee may extend into the riser for venting.

(4) Grease interceptor intercompartmental wall fittings.

(a) All grease interceptor intercompartmental wall fittings must extend into the liquid to a point between six inches and twelve inches from the bottom of the tank.

(b) If slots or ports are used as intercompartmental fittings:

(i) The location of the slot or port must be at the same depth as the bottom of outlet tees or baffles; and

(ii) The opening must have a minimum area of twelve square inches with a minimum vertical dimension of three inches.

(5) Grease interceptor intercompartmental walls. Grease interceptor intercompartmental walls must:

(a) Restrict solids from moving from one compartment to the other except through the intercompartmental wall fittings; and

(b) Withstand pumping of the adjacent compartment without risking structural damage or functional failure.

(6) Grease interceptor tank liquid depth. Grease interceptor tanks must contain a liquid depth of not less than three feet.

[Statutory Authority: RCW 43.20.050 (2) and (3). WSR 09-23-119, § 246-272C-0230, filed 11/18/09, effective 12/19/09.]