The approved design for grease traps shall be as follows:
The grease trap must be constructed in accordance with the current plumbing codes adopted by the City of Austin, as amended, and installed in a manner acceptable to the Watershed Protection and Development Review Department (no exceptions).
The grease trap shall have two compartments.
While operating at the trap's rated flow capacity, the first compartment must provide a retention time of no less than seven minutes, and the second compartment must provide a retention time of no less than five minutes.
Trap inverts and vents shall be external to the compartments.
The flowline to the trap (upstream of inlet invert) must be at least 3 inches above the static water level of the tank.
Similarly, the trap vent must be at least 3 inches above the static water level of the tank
The trap inlet must be near an elevation that is one half of the height of the tank's static water level, and the trap outlet must be at least 12 inches above the floor of the tank.
Adequate flow diffusion features must be provided to evenly distribute flow throughout the grease trap. Examples of such features would include a flow diverter plate in the primary compartment, "tee" piping between the two trap compartments and "tee" piping on the tank outlet.
Each trap compartment shall be accessible for cleaning and inspection purposes (no exceptions).
Exceptions to certain of these criteria may be considered for approval in conjunction with the Plan Review process. In such cases, engineering drawings and supporting performance data must be submitted to and approved by the Director prior to grease trap installation. Historically, metal grease traps of alternative designs have been approved for those sites needing grease traps of 250 gallons or less.