Why Correct Sizing Matters
Correct sizing gives wastewater enough treatment capacity while maintaining usable drainage. An undersized interceptor can pass FOG and require frequent cleaning. An oversized or poorly placed unit can increase cost and complicate maintenance.
Sizing Inputs
Sizing may use:
- Fixture dimensions and compartment volumes
- Fill factor and drainage period
- Rated appliance discharge
- Grease-waste pipe diameter
- Drainage fixture units
- Expected simultaneous flow
- Hydromechanical or gravity-interceptor design
- Manufacturer ratings and approved standards
The applicable plumbing code and authority having jurisdiction determine the accepted method.
From Calculation to Installation
We connect the sizing result to pipe elevations, venting, flow control, access, covers, excavation, and pump-truck clearance. Final equipment selection must be approved through the project permit process.
Frequently Asked Questions
Can seating count alone size an interceptor?
Not reliably. Fixture load, flow, drainage time, menu, operating practices, and local requirements all matter.
Who approves the final size?
The authority having jurisdiction approves the permitted design. Our calculations support that review.
Request a Sizing Review
Request Grease Interceptor Sizing from Seattle Plumbers for documented loads, code-aware calculations, and coordinated installation planning.