Commercial Plumbing for Restaurants and Grocery Stores: An Owner's Guide

Grease Interceptors and FOG Compliance

Every restaurant in the Denver metro is required to have a grease interceptor (also called a grease trap) sized appropriately to its kitchen output. The interceptor sits between your kitchen drains and the city sanitary sewer, slowing wastewater flow enough that fats, oils, and grease (FOG) cool, separate, and float to the top where they can be pumped out before the water continues to the sewer.

The local Wastewater Authority (Metro Water Recovery, formerly Metro Wastewater Reclamation District for most of the metro) enforces FOG compliance through a permit program. Restaurants are inspected, and violations can result in fines, mandatory upgrades, and in repeat-offender cases, sewer service termination. The permit requires:

• A properly-sized interceptor based on your kitchen's drainage fixture units
• Regular pumping (typically every 30–90 days depending on volume)
• Documentation of every pump-out, kept for inspection
• Use of an approved licensed grease hauler for disposal

The most common violation we see is undersized interceptors. A restaurant grows over time — adds equipment, expands the menu, increases volume — but the original interceptor was sized for a smaller operation. The interceptor fills faster, FOG escapes to the sewer, and eventually a passing inspection catches it. Upgrading proactively is far cheaper than paying fines and emergency replacement.

The second most common: not pumping often enough. A grease interceptor that's more than 25% full by volume of FOG and solids has lost most of its effectiveness. Going on a quarterly schedule when you should be on monthly is how most restaurants end up with FOG violations.

Floor Drains and Trap Primers

Commercial kitchens and grocery stores have far more floor drains than residential buildings — typically one near every food-prep station, every dishwashing area, and every walk-in cooler/freezer. Each one needs a properly-sized trap to keep sewer gas out of the building.

The catch: floor drain traps dry out if they're not used regularly. A floor drain in the back corner of a walk-in cooler that nobody walks past for three weeks will lose all its trap water through evaporation, and now sewer gas has a direct path into your store.

Trap primers are the solution. These small valves automatically inject a tiny amount of water into the trap whenever a nearby fixture is used (or on a timer), keeping the seal intact. Code requires them in commercial buildings — but they're frequently missed during build-out, fail silently, or get disabled during renovations.

If your store has a chronic sewer smell that comes and goes, the most likely cause is a dry floor drain trap. Check whether it has a trap primer, whether the primer is functional, and whether someone needs to manually pour water into rarely-used drains every few weeks.

Refrigeration Condensate

Every refrigeration case, walk-in cooler, walk-in freezer, ice machine, and HVAC system in your store generates condensate water. That water has to go somewhere — and where it goes matters for code, for sanitation, and for floor safety.

Refrigeration condensate is technically considered "clear water waste" by code, which means it can drain to a floor drain rather than directly to the sanitary sewer. But it can't simply trickle to the floor — pooled condensate is a slip hazard and a health code violation.

Best practice for handling condensate:

• Each refrigeration unit's condensate line drains to an indirect waste fixture (typically a floor sink) with an air gap to prevent backflow contamination.
• Condensate lines are sloped properly (1/4 inch per foot minimum) and supported regularly to prevent sagging.
• Lines are insulated where they pass through unconditioned space to prevent condensation forming on the line itself.
• Floor sinks are accessible for cleaning and have removable strainers.
• A maintenance schedule includes flushing condensate lines quarterly to prevent algae and slime buildup.

Common failure: A walk-in freezer condensate line that gets clogged or freezes will back up into the freezer, creating ice on the floor and eventually shutting the unit down. We see this several times each winter in the metro.

Ice Machines and Backflow Prevention

Ice machines have specific plumbing requirements beyond a typical fixture: they need a dedicated water supply with a shutoff, a backflow preventer (typically a built-in or inline check valve), a drain line to a floor sink with an air gap, and condensate handling (for the unit's compressor cooling).

The backflow protection matters because ice is technically a food product, and contamination of the water supply at the ice machine could contaminate ice that's served to customers — a health code violation with serious consequences.

Most ice machines come with built-in backflow protection, but it has to be supplemented with proper installation: an air gap on the drain (not a hard pipe connection), and a dedicated supply line with a serviceable shutoff. The drain needs to be clear and the air gap needs to be visible during health inspections.

Filtration matters too. Denver's hard water scales up ice machine evaporators quickly, reducing efficiency and ice quality. A scale-reduction filter on the ice machine supply is one of the cheapest preventive measures available — typically $80–$200 per filter cartridge with annual replacement, vs. $2,000–$5,000 to descale or replace a fouled evaporator.

Sanitary Sewer Sizing for High-Volume Commercial

A grocery store or busy restaurant generates dramatically more wastewater than a residential building — and the building's drain system has to be sized accordingly. The original construction may have been sized for the building as it was first built; if the use has changed (a retail space converted to a restaurant, for example), the existing drain piping is often undersized for the new use.

Symptoms of undersized sanitary sewer:

• Slow drains throughout the building during peak hours
• Backups during peak hours but no problems off-peak
• Floor drain backups in the kitchen or back-of-house when multiple sinks drain simultaneously
• Recurring main line clogs even with a clean sewer line and properly-sized grease interceptor

If you're seeing any of those, an evaluation by a commercial plumber is worth doing. Sometimes the fix is hydro-jetting and a maintenance schedule. Sometimes it requires upsizing branches or the main. Either way, knowing the actual situation beats living with chronic problems.

What to Look For in a Commercial Plumber

Restaurant and grocery store plumbing is specialized work. The right plumber for your operation should:

• Have direct experience with grease interceptor sizing, installation, and pumping logistics
• Understand your local Wastewater Authority's FOG permit requirements and inspection process
• Be familiar with Health Department requirements for floor drains, ice machines, and indirect waste
• Be available for emergency calls (because your operation can't shut down for two days waiting for service)
• Maintain detailed documentation suitable for health and FOG inspections

If a plumber doesn't routinely work in restaurants, they're going to learn on your job — and the learning curve costs you in violations, re-work, and downtime.

Frequently Asked Questions

How often does a restaurant grease interceptor need to be pumped?

Pumping frequency depends on the size of the interceptor and the volume of FOG your kitchen generates. Most restaurants in the Denver metro pump every 30–90 days, with high-volume operations pumping monthly. Local FOG ordinances require the interceptor to remain less than 25% full of FOG and solids — exceeding that threshold is a violation regardless of your scheduled frequency.

What's the difference between a grease trap and a grease interceptor?

The terms are often used interchangeably, but technically a grease trap is a smaller under-sink unit (5–50 gallons) suitable for low-volume operations, while a grease interceptor is a larger in-ground or large-format unit (250+ gallons) sized for full restaurant kitchens. Most full-service restaurants in Colorado require an interceptor — under-sink traps are typically only allowed for very low-FOG operations.

My grocery store has a constant sewer smell — what's likely causing it?

The most common cause is a dry floor drain trap somewhere in the building. Trap primers may have failed or never been installed properly. Walk-in coolers, walk-in freezers, and back-of-house drains that aren't used regularly are the usual culprits. A commercial plumber can identify and address the source — and recommend trap primer installation if missing.