How long does a grease interceptor last?

No code, city document or trade body we found gives a set lifespan for a grease interceptor. The only numbers come from a manufacturer that sells polyethylene tanks.

### What number does a manufacturer give?

Schier Products says on its own site that food waste decays inside an interceptor and makes hydrogen sulfide gas that eats away at steel and concrete from the inside out. It then says the average lifespan of a concrete grease interceptor is 10 years, and that steel interceptors average five. The page cites no study for those figures. Schier also sells plastic units, so treat the numbers as a sales claim, not a measured average.

The concrete side does not give a number either. The National Precast Concrete Association (NPCA) says precast concrete interceptors offer structural integrity, design flexibility and a long service life. It does not say how many years that is.

### Why is there no official number?

Because the tank is not what usually decides. The NPCA says performance and protection for the sewer downstream depend on how the tank is used. Zurn, a maker of small steel interceptors, puts it this way in its care sheet: no matter how efficient the design or how proper the installation, grease interceptors perform only as well as the maintenance routine allows.

So two identical tanks can age very differently. One gets pumped on time, the baffles stay in place and the lid seals. The other sits full, turns sour and rots.

### What do cities say about replacing one?

Cities do not set an age. They look at condition.

• Phoenix. During an inspection the inspector checks the interceptor to see if any parts are missing or if the interceptor itself has rotted out and needs to be replaced. If something is wrong, the inspector issues a requirement to clean, replace or repair and sets a time frame.
• Phoenix code. Chapter 28 says interceptors must be kept in continuously effective operating condition, and that includes necessary repairs to internal structures.
• Tempe. Inspectors want grease control devices in good condition with no holes, missing or broken parts or severe corrosion.
• Mesa. Interceptors must be constructed of impervious materials, be of substantial construction, and be watertight.

That is the real test. If the tank holds water, keeps its parts and does its job, no city on this list says it is too old.

Most early failures trace back to a short list of causes. Some are slow, like acid damage. Some happen overnight, like a lid that gives way.

### How does acid damage a tank?

This is the big one for concrete and steel. Food waste decays inside the tank and gives off hydrogen sulfide gas, and Schier says that gas eats away at steel and concrete from the inside out. The Plumbing and Drainage Institute (PDI), a trade body of drainage product makers, names sulfuric acid as part of the same damage.

You do not have to take a manufacturer's word for it. Training slides from the California Regional Water Quality Control Board, Colorado River Basin (2010), show a slide headed "Interceptor deterioration, baffle wall collapse, leaking, and corrosion impact to public sewer," with the note that the wastewater pH in that interceptor was 1.5. For scale, pH 7 is neutral, and lower numbers are more acidic. The same slides say one of the main reasons for a certification program for interceptors is deterioration or leaking tanks.

The NPCA's care guide points the same way in a quieter voice. It warns against letting excessive corrosive agents drain into the interceptor, and it says settled material should be vacuumed out at each cleaning to prevent biological breakdown and the unwanted release of gases.

### Does skipping or shortchanging pump-outs shorten the life?

Yes, and the state slides say why. They report that studies show partial pump-outs let food solids build up, which can cause short-circuiting, more tank deterioration and a lower pH. Short-circuiting means water rushes through without time to separate.

The same slides say to make sure the outlet tee, inlet tee and mid-wall baffle sweep are all back in place after pumping. A pump-out is a chance to look at the tank, not only to empty it. Phoenix's manual agrees: it tells owners to witness the cleaning to make sure the pumper cleans the tank completely, and to check for damaged or missing parts while it is open.

For the schedule your city sets, see the 25 percent rule page and the Phoenix pump-out schedule.

### What about broken baffles and tees?

Baffles and tees steer the flow through the tank so grease has time to separate. The NPCA says the inlet tee extends below the waterline to prevent excessive turbulence, and the treated water leaves through the bottom of the effluent tee. When a part cracks or falls off, the tank cannot work as designed. We cover how to spot that on the broken baffle and tee page.

### Can oversizing hurt a tank?

It can. PDI says field experience showed that oversizing can result in hydrogen sulfide gas and sulfuric acid that destroy the interceptor and the drainage system. Bigger is not always better. Sizing is covered on the sizing worksheet page.

### What about lids, gaskets and covers?

A worn cover is a safety problem as well as a leak. The NPCA notes that gravity interceptor lids are often brought to grade, so an improperly secured or damaged lid raises the risk of someone falling into the tank. It says to check the gasket and replace it if it is cracked or broken, and to keep a spare gasket on site. Its guide also warns never to enter the interceptor to do maintenance. See the lid and traffic rating page for cover choices.

Look for the clues at three moments: during a pump-out, during a city inspection and in between.

### What should you check at a pump-out?

The NPCA's guide lists a few checks:

1. 1Note the liquid level before the tank is pumped. An unexpectedly low level could mean a leaky tank.
2. 2Note whether the level is unexpectedly high or grease sits above the normal level. That could mean a plugged fitting, line or filter.
3. 3After pumping, look at all fittings, baffles and fixtures inside to see that they are in good working order.
4. 4Check the access covers and gaskets.

Phoenix's manual adds that the inspector counts the fixtures and checks how much grease is in the tank to see if the current schedule works. Ask the pumper to point out any cracks, soft or flaking concrete, or missing parts, and keep the service ticket. Records must be kept on site for three years in Phoenix.

### What are the warning signs between visits?

• Grease or wastewater showing up in a floor sink. The floor sink backup page covers first steps.
• Odor that returns fast after a pump-out. The NPCA says most odor problems come from improper venting of the building's plumbing, so check that before blaming the tank. See the smell page.
• A liquid level that is different from last time.
• Grease turning up in the line past the tank. See the sewer lateral page.

Replacement is a permitted job. Phoenix says every grease interceptor installed or replaced goes through plan review, and a like-for-like swap of a small hydromechanical unit can be submitted over the counter. The permit page covers each city, and the installation steps page walks the job from plan review to first pump-out.

### Does the material matter?

For big tanks, cities set the rules on what is approved. Phoenix keeps a list of approved gravity interceptors and requires them to be designed by a registered engineer and IAPMO certified. For small hydromechanical units, Phoenix requires a corrosion resistant material, either stainless steel or polymer. Zurn's steel units are coated with an acid-resisting epoxy. Whatever the material, the maintenance routine sets the pace. For risers and lids, see the riser extension page.

### How does this fit with the other pages on failure?

If the tank is fine and the problem is water backing up, try the floor sink page or why a grease trap keeps overflowing. To see what a city inspector checks, read what city inspectors check.

Call a licensed plumber when a pump-out shows a cracked wall, a missing baffle or tee, a bad cover, or a low liquid level, and when a failed interceptor has to be repaired or replaced under a permit. A plumber can fix or replace plumbing parts, and the city plan reviewer will want the work shown on the drawings. Our plumbers are licensed and insured, we give free estimates with upfront pricing, and we run 24/7 emergency service if grease is backing up during service. Start at our commercial plumbing page.