Septic System Information to answer the pressing question: Can bathroom flows be added to a grease trap?

Based on a strict reading of the Title 5 requirements, bathroom flows are not appropriate for grease traps. 15.230(2) Grease traps shall be installed on separate building sewer…
The greatest difference between a Grease Trap and a Septic Tank is the outlet tee:
15.230(5) …The outlet tee shall extend to within 12 inches of the bottom of the tank.
15.227(6) …The outlet shall be provided with a tee extending below the flow line in accordance with the following table: Liquid Depth in Septic Tank Depth of Outlet Tee below Flow Line
5 feet 19 inches
6 feet 24 inches

On the other hand, this system was constructed in the 1980s. The grease traps were installed under a repair. Is there room for leniency based on any form of grandfathering?

15.230: Pretreatment Units - Grease Traps
(1) Grease traps shall be provided for kitchen flows at restaurants, nursing homes, schools, hospitals and other facilities from which grease can be expected to be discharged.
(2) Grease traps shall be installed on a separate building sewer serving kitchen flows into which the grease will be discharged. The discharge from the grease trap must flow to a properly designed septic tank or to a building sewer prior to the septic tank.
(3) Grease traps shall have a minimum depth of four feet and a minimum capacity of 1,000 gallons, and shall have sufficient capacity to provide at least a 24-hour detention period for the kitchen flow. Kitchen flow shall be calculated in accordance with 310 CMR 15.203.
(4) Grease traps shall be watertight and constructed of the materials specified in 310 CMR 15.221 and 15.226(1) and (2).
(5) The inlet tee shall extend to the mid depth of the tank. The outlet tee shall extend to within 12 inches of the bottom of the tank. Tees shall be Schedule 40 PVC and properly supported by a hanger, strap or other device.
(6) Grease traps shall be installed on a level stable base that has been mechanically compacted and onto which six inches of crushed stone has been placed to minimize uneven settling.
(7) Grease traps shall be provided with a minimum 20-inch diameter manhole frame and cover to grade over the inlet and outlet tees.
(8) Grease traps shall be accessible for inspection and maintenance. No structures shall be constructed directly upon or above the grease trap access locations.
(9) The invert elevation of the inlet of a grease trap shall be at least two inches above the invert elevation of the outlet. The inlet and outlet shall be located at the center line of the tank, and at least 12 inches above the high groundwater elevation.
(10) Backfill around the grease trap shall be placed in such a manner as to prevent damage to the tank.
(11) Grease traps shall be maintained in accordance with 310 CMR 15.351.
(12) Grease removal by other devices located within the building as part of the internal plumbing are not within the jurisdiction of 310 CMR 15.000, shall not be considered for compliance with 310 CMR 15.230 and shall comply with the State Plumbing Code. Grease removal devices located outside of the building, other than those in compliance with 310 CMR 15.230, require the prior written approval of the Department.
(13) The Approving Authority may require that alarms and/or remote monitoring devices be installed and connected to grease traps.

15.227: Placement and Construction of Tees [in septic tanks]
(1) Inlet and outlet tees shall be Schedule 40 PVC and shall extend a minimum of six inches above the flow line of the septic tank and be on the center line of the septic tank located directly under the clean-out manhole. Tranverse flow baffles shall not be used as substitutes for inlet or outlet tees.
(2) The minimum separation between inlet and outlet tees shall be no less than the liquid depth of the septic tank and shall be the longest direction (which shall not include the diagonal distance) across the tank in plan view.
(3) Inlet and outlet tees to rectangular tanks shall be set in the end walls or into a side wall within 12 inches of the end wall. For circular tanks, the inlet and outlet tees shall be set and stabilized on opposite ends of a diameter of the tank.
(4) There shall be an air space of at least three inches between the tops of the tees and the inside of the tank cover. The tops of the tees shall be left open to provide ventilation or separate ventilation shall be provided. All outlet tees shall be equipped with a gas baffle or a Department approved effluent tee filter.
(5) The inlet pipe elevation shall be no less than two inches nor more than three inches above the invert elevation of the outlet pipe. The inlet and outlet invert elevations shall be at least 12 inches above the high groundwater elevation. If high groundwater (redoximorphic features) is determined by soil evaluation in accordance with 310 CMR 15.100 through 15.107 at the proposed location of the septic tank, the Approving Authority may reduce the 12 inch required separation, but in no cases shall it be reduced to less than one inch above high groundwater as determined by redoximorphic features.
(6) The inlet tee shall extend a minimum of ten inches below the flow line. The outlet shall be provided with a tee extending below the flow line in accordance with the following table: Liquid Depth in Septic Tank Depth of Outlet Tee below Flow Line
4 feet 14 inches
5 feet 19 inches
6 feet 24 inches
7 feet 29 inches
8 feet 34 inches
(7) Effluent tee filters may be installed in lieu of outlet tees provided that they are installed in accordance with the manufacturer’s specifications, include an appropriate outlet cover at grade, and are inspected and cleaned at least on an annual basis.

1985 Design Plans by Leonard Design Associates and Schofield Brothers
1 2 3 4 5
As-built cards from BOH
Title 5 Inspection (1996)
Other documents from BOH