Placement and Construction of Tees

(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.