Norwesco 1250 Gallon Plastic Two Compartment Septic Tank - IAPMO Certified

Why two compartments

A two compartment tank gives the solids a second chance to settle before the effluent reaches the drainfield, which is why many states and counties require it on a new system. Whether yours does is set by the design your installer or engineer is working to and by the local code. Our guide to single compartment versus two compartment septic tanks lays out the difference and who requires what. For the approvals themselves, including how IAPMO and the Canadian CSA B66 listing relate to US plumbing codes, see our note on Norwesco IAPMO and CSA B66 septic tank approvals. Size the tank to the house or the load with the tank sizing calculator and the tank sizing guide, then check the result against the county's own minimum, which wins.

Putting it in the ground

Follow Norwesco's installation instructions for this tank for the excavation, the bedding, the backfill material and the water filling sequence; the instructions are specific to the shell and your inspector will expect them. The universal points: the excavation floor has to be flat along the full 116 inch length, because a moulded tank bears where it touches and a void under one end is carried by the wall; the tank needs to be filled with water as it is backfilled, both compartments together, so the walls and the baffle are supported from both sides; and the inlet has to sit higher than the outlet so the system flows by gravity. Depth of cover, traffic loading, groundwater and risers are set by the drawing for your site and by your installer, not by this page. Set the tank so the inlet end is at the house side; a two compartment tank only works one way round.

Openings and fittings

1. Inlet. A 4 inch adapter with a PVC tee assembly, into the first compartment. The tee directs the incoming flow down below the scum layer.
2. Outlet. A 4 inch adapter with a PVC tee assembly, out of the second compartment. The outlet tee draws from the clear zone between the scum and the sludge, which is what keeps solids out of the drainfield.
3. Manway. A 20 inch gasketed manway for pumping and inspection. Both compartments get pumped, so tell the pumper it is a two compartment tank.
4. Drawing. Norwesco's drawing for this tank, linked under Technical Drawing on this page, shows the inlet and outlet invert heights, the baffle position and the manway location for setting the tank to grade.

The rest of the family

Same shell with one compartment: the 1250 gallon one compartment septic tank. Same two compartment tank supplied with adapters and two covers: the 1250 gallon two compartment septic tank with adapters and 2 manhole covers. One size down: the 1000 gallon septic tank. One size up: the 1500 gallon septic tank.

Shipping and receiving

The tank ships LTL, NMFC 156600-02, from Norwesco's Hanford, California plant. On the trailer it is 116 by 55 by 70 inches and 387 lb. The listed price is before freight; the freight cost estimator gives the lane cost to your ZIP, and because this tank ships from one plant, the lane matters more than usual to the total. At the tailgate, check the part number 41744 against the bill of lading, check that both tees and the manway lid are present, and look over the shell for transit damage before the driver leaves.

Questions before you order? Call 866-418-1777 with your county and the system design.