A waterless urinal should not smell like sewage when it is maintained. Its odor seal is a floating sealant layer, so the usual causes are a cartridge that has run out of sealant, a drain line coated with urine deposits, or cleaning that washed the sealant away. Check the sealant first.
How a waterless urinal blocks sewer odor
A flush urinal holds a plug of water in its trap. A waterless one has no water, so it uses a liquid instead. Waterless Co., a manufacturer, describes "a vertical trap or cartridge filled with a thin layer of liquid sealant that sits atop the drain area of the urinal." Sloan describes the same idea for its cartridge: waste "passes through this sealant which isolates foul odors from the restroom."
Codes treat that sealant as the trap seal. Minnesota's rule amending subsection 412.1.1 of the Uniform Plumbing Code says: "Nonwater urinals shall have a barrier liquid sealant to maintain a trap seal." Lose the sealant and you have lost the seal. For the pros and cons of the design overall, see waterless vs flush urinals.
Cause 1: the sealant is gone or the cartridge is spent
Sealant leaves a little at a time. Klaus Reichardt of Waterless Co. writes that "As the urinal is used, small amounts of the sealant will be drained into the waste line and need to be replenished." Sloan's spec sheet says its cartridge is "engineered to last for an average of 7,000 uses," so a busy restroom outruns it. For odor calls, Sloan's maintenance guide gives a simple check: dip a rolled-up corner of paper towel into the top of the cartridge. "If the paper towel comes out clean or without blue sealant, change the cartridge."
Some fixtures skip the cartridge. Zurn's Z5795 sheet describes a urinal where you "fill trap with Zurn AquaGreen sealant," so the same rule applies to the sealant in that trap.
Cause 2: water or cleaner pushed the seal out
Sealant floats, so it can be rinsed away. The Buildings cleaning guide warns: "Do not pour excess or soiled water down the waterless urinal trap - it can flush the sealant out of the trap insert." A bucket of water poured down the fixture can do exactly that.
Chemicals matter too. Waterless Co. says abrasive cleaners and harsh chemicals "should be avoided" because they can damage the trap or cartridge system and the finish. CleanLink's article on cleaning these fixtures adds that scratches from bristled brushes or harsh chemicals make small cracks that "can harbor germs and odors." Use the cleaner the manufacturer names, mist it on, and wipe.
Cause 3: deposits in the drain line
With no rinse water, urine leaves residue in the pipe. Sloan explains that a soft substance called struvite forms in urine without water, and says: "Struvite can form in drain lines over time, however, it is water soluble and only requires water to clean." That is why Sloan pairs cartridge changes with drain-line flushing, and why its cartridge-change steps include scrubbing the housing and flushing it with hot soapy water.
Layout counts here. Minnesota's amended UPC subsection says a water-supplied fixture must sit upstream of a nonwater urinal "at the end of that same drainage branch." Hawaii's 2021 code says the upstream fixture is there "to facilitate drain line flow and rinsing." Sloan also lists an improperly pitched drain line and a clogged housing among the reasons a urinal drains slowly. Your city's adopted plumbing code and amendments control, so confirm them before a retrofit.
Cause 4: the smell is not from the urinal
Sloan's own odor checklist includes: "Odor not coming from urinal. Check other sources of odor such as air vents, toilets, trash receptacles or floor drains." It also lists a loose clamp on the urinal's drain connection. Floor drains are on that list, and how their traps stay sealed is covered in trap primers for commercial floor drains. A smell that spreads beyond the restroom is covered in sewer gas smell in a commercial building.
A check order that saves time
- 1Test the sealant with the paper towel trick.
- 2Check how long it has been since the last cartridge change, against the manufacturer's use count.
- 3Watch drainage: Sloan lists a full cartridge, a cartridge not locked in place, a drain line that is not pitched correctly and a clogged housing or drain line among the reasons a urinal drains slowly.
- 4Look at the drain clamp and the fixtures around the urinal.
If the sealant and cartridge are fine and the smell persists, the problem is in the drain or vent side. HQ handles commercial restroom plumbing across the Valley, licensed and insured, with free estimates and upfront pricing. A written schedule for cartridge changes belongs in a commercial plumbing preventive maintenance plan.