On the Offensive

by Katie Lee

How to locate and eliminate offensive plumbing odors.

By Tatiana Cohen

Offensive plumbing odors can cause customers not to return to your business. These odors normally originate in drain and/or vent lines in your facility and can be very hard to locate and eliminate. So, the question is “how can an odor be located and eliminated?”

To solve odor problems, the odors need to be identified, labeled and understood. It takes experience to know the difference between sewage, grease, mildew and other types of odors. If you are not familiar with each of these “smells,” you can still locate the source and make the necessary repairs. The following are hints to recognize the most common odors.



Sewage often is a bitter smell and can be confused with grease-trap odors (or vise-versa). Once you have been around these odors enough, you will be able to distinguish between the two. Sewage odors come from drain lines that unintentionally release sewage gas into a restaurant, retail store, or indoor or outdoor spaces. The following are areas to inspect to determine the source of the odor leak:

• Inspect all sinks (floor and counter) and drains to make sure they have standing water in the P-trap (see diagram). P-traps are designed to retain water, making a “water seal” which blocks odors and bugs from re-entering the inhabited space. If the P-trap fixture is broken, its water will leak into the ground or possibly the tenant space below, allowing odors and/or bugs to escape. If this happens, the P-trap will need to be replaced. If a P-trap is not used for an extended period of time, the water seal will evaporate, and odors will be released. The easy solution to this is to simply fill the P-trap with water, re-establishing the water seal.

• Inspect all cleanout locations. Cleanouts have service plugs (see diagram) screwed into the drainage pipe under the clean-out cover. The plugs need to be without flaw/holes, preventing gases from escaping. If the plug is damaged, even the smallest blemish will cause odors to escape. Screws that hold the decorative cover in place should not penetrate all the way through the cap and into the drainage pipe. This can lead to deterioration of the screw due to the vent gases. Remember there are floor and wall cleanouts and sometimes these cleanouts can be mistakenly abandoned and built over (mostly in wall cleanouts). These forgotten cleanouts, when in the wall, can be found by looking above the ceiling line, locating the vent line and tracing it back down the wall to see if a fitting exists and leads toward the wall but is not visible at the base of the wall.

• Inspect the cleanout plug behind the decorative cover to see if there are multiple screw holes holding the decorative cover in place. It is very common that multiple screw holes will be found on the inner plug.

• Inspect wax rings on all toilets as they may not be seated correctly and can emit odors when not seated properly.

• Inspect above ceiling line for any opened/abandoned vent pipes.

• Verify that the tops of vent lines on the roof are higher than the parapet walls to allow odors to be swept away by a small breeze. HVAC or MUA units too close to a vent pipe can pull odors into the building. If raising the vent pipe over the equipment doesn’t solve the problem, a charcoal filter (brands like Sweet Air and Studor are the most common) can be installed on the roof vent pipe.

• Inspecting a drain line in the area of question via camera can provide information to find the problem, but you need a plumber who knows what to look for and a color camera makes it even easier.

If the above tips have not worked, a plumber can perform a smoke test to locate any breaks in drain and/or vent lines. Make sure when performing a smoke test, the plumber uses a high powered smoke machine and not a smoke bomb (a large amount of smoke will be needed; so much so, that the roof vents should billow out smoke like a factory smokestack). While a smoke bomb can work, it requires more effort and luck to find the problem. When using a smoke bomb, all vent lines need to be capped in order to contain the smoke and force the smoke to exit the breached area; again, smoke bombs are not the best options. When performing any type of a smoke test the building need to be vacant of guests and will require a team of two to four individuals searching for the leak. The use of a laser light can be very helpful reflecting the beam of the smoke and identifying the source. Before performing any smoke test, make sure your neighbors aware and your plumber contacts the local fire department.


Grease Trap Odors

Many confuse a grease trap odor with a sewage odor, even though they are two different odors. To find this odor:

• Validate the grease trap is in proper operation and not magnifying the source of the problem. If a grease trap odor is stronger than normal, it is possible that the baffles or transfer pipe within the trap are clogged and/or damaged and will need a plumber to repair.

• Inspect cleanouts on the inlet and outlet of the in-ground grease trap. A cleanout will have a service plug screwed into the drainage pipe below the finished cover. Verify that the service plugs are without flaws or holes and are properly secured in place.

• Inspect all grease trap covers, checking to see that they have no holes in the trap lid that can allow odors to escape. The trap lid should say “interceptor” on it. If the trap still emits odors, apply a thin coat of silicone around the lid to stop gases from exiting through the perimeter ring; however, this process will need to be performed every time the lid is pulled and is not a long term solution. Another option would be to install a trap cover plug cover. A trap cover plug is a giant disk that slips under the trap lid like an oversized cleanout service plug which will hold down the odors.

• Verify that the grease trap riser ring that secures to the trap is securely mounted and is not cracked or broken. Grease traps that are located in planter are sometimes set in a hurry and are not secured to the trap, allowing odors to seep out.

• Make sure that the in-ground grease trap has a vent pipe and is not venting in an area where odors can’t escape and blow away.

• Pipe connections at the grease trap can shift and allow odors to escape. While not visible, a smoke test would help determine if a separation has occurred.


Indoor Odors

Indoor odors can be a mixture of grease trap, sewage gas, mildew, vomit, stagnant water and more. While already addressed how to locate grease and sewage odors, let’s look at some other nuisance odors:

Stagnant Odors: Stagnant odors can come from:

• Water sitting under damaged or old tile.

• Between the cove base tile and wall.

• Plumbing line leak within a wall or cabinet.

• Soda/beer chase line filled with water.

Mildew Odor: Mildew odor is relatively easy to find as it is also visible in the area the odor is coming from. Mildew can be caused by mold developing in a wall or cabinet where water collects over time.


P Trap Drawing

Outdoor odors can come from grease traps, natural gas or stagnant odors. While we already addressed how to locate grease odors, let’s look at some others.

Natural Gas: Natural gas can be from in-ground patio heaters that have rusted, allowing natural gas to escape. This will require immediate repair by a plumber.

Stagnant Odors Outside: Patio drains typically do not have P-traps due to the risk of having water freezing in the trap, causing it to break. With the patio drains not having P-traps, and steady water flow, debris and sludge can get stuck in the pipe causing the odor to build up and escape into the patio. A solution for the patio drain odors is to thoroughly hydro jet the lines to the city main or common area.


— Tatiana Cohen is the national accounts sales manager for TNT Products LLC, which distributes the Guardian Drain Lock products. Email the author at [email protected].

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