Repair when the failure is an internal part such as a baffle, tee or fitting, or a lid or riser, and the tank shell is sound. Replace when the shell is rotted, cracked through, leaking or showing exposed steel, or the tank is too small for the kitchen it serves. In Phoenix, a replacement goes through plan review first.
When is repair the right call?
When the shell is sound and the failure is something inside or on top of it. Phoenix's own rules treat this kind of fix as ordinary maintenance. Section 28-15 says interceptors must be kept in "continuously effective operating condition at all times," which includes "necessary repairs to internal structures." If the baffle, the inlet fitting or the outlet tee is cracked, loose or gone, that is a repair. So is a damaged cover, frame or riser ring.
The NPCA's guidance explains why those small parts are worth fixing: "An inlet baffle or diverter is necessary to increase the retention time and avoid short-circuiting," and "An outlet baffle or tee is necessary." A tank with a good shell and a broken tee is a repair job, and fixing it restores the flow path the tank was designed around. See what happens when a baffle or tee breaks for how the failure shows up.
When is replacement the right call?
When the shell itself has failed or the tank cannot do the job it is asked to do. Phoenix's manual says its inspector checks whether "any parts are missing or if the interceptor itself has rotted out and needs to be replaced." San Antonio's inspection checklist gives a concrete test: the interceptor "does not have cracks or defects (or you can see exposed steel in the walls and floor)." Cracks that go through the wall, exposed rebar or steel, and a tank that leaks all point toward replacement. Mesa's code says interceptors must be "watertight," and a shell that cannot hold water has stopped meeting that rule.
Our page on why concrete interceptors corrode explains what rotted concrete looks like, and when coating or lining is realistic and when it is not.
What about a tank that is too small?
A repair cannot fix an undersized tank. If you added a dishwasher, a disposal or more prep sinks since the tank was set, the tank may be sized for a smaller kitchen than the one you run.
Phoenix sizes gravity grease interceptors from the grease-bearing drainage fixture units. Its amended plumbing code multiplies the total fixture units by 3 gallons per minute and then by a 12-minute retention time, or a 17-minute retention time with food waste disposers. Mesa's code sets "a capacity of five hundred (500) gallons" as the minimum size for all interceptors and requires "at least two (2) chambers." Our page on how to size a grease interceptor for a restaurant walks through the worksheet.
If the tank is the right size and keeps overflowing, look at the parts, the pump-out schedule and the line before you blame the shell. If the kitchen outgrew the tank, replace it.
How do the two paths compare?
| Repair | Replacement | |
|---|---|---|
| Typical trigger | Broken baffle, tee, fitting, lid or ring | Rotted, cracked or leaking shell; exposed steel; undersized tank |
| Order of work | Hauler pumps, crew enters, part is fixed | Plan review, then hauler pumps, excavation, new tank, reconnect |
| Permit in Phoenix | Ask your city; internal repairs are maintenance | Plan review required |
| Disruption | The kitchen's drains are affected while the tank is open | Longer, with digging in the lot or alley |
On the permit row, Phoenix says "all grease interceptors installed and replaced in the City of Phoenix must go through plan review," and notes that like-for-like replacements of hydromechanical interceptors can be submitted over the counter. The plan review is where the city confirms "that the grease interceptor that is being installed is sized correctly, approved for use in the City of Phoenix, and that all grease bearing fixtures are plumbed to the interceptor." Our page on whether you need a permit to replace or add an interceptor covers the Valley cities, and what installing an interceptor involves covers the new-tank work.
How do you actually decide?
Get the inside of the tank documented first. Four steps:
- 1Pump the tank and get a written inspection with photos. A repair-or-replace answer given from the surface is a guess. See what a plumber checks inside a grease interceptor.
- 2Separate the parts from the shell. List each defect and mark it as a part or the shell.
- 3Check the size against today's kitchen. Count the grease-bearing fixtures and compare.
- 4Ask for both options in writing. A repair quote and a replacement quote, with what each includes, so you can compare the same things.
Mind the clock. When a city inspector finds a problem, Phoenix's manual says the inspector "will prescribe a time frame for the requirement to be completed," based on the impact on the sewer system and the work involved, and that "Extensions can be granted based on business needs if the request is in writing." If replacement is going to take plan review, start the paperwork right away.
HQ repairs and inspects grease interceptors, including baffles and inlet and outlet fittings, and the job runs with a three-person confined-space crew. We do not pump; a licensed hauler empties the tank first. HQ gives free estimates with the price upfront before work begins.