Usually a slimy film of sugar, bacteria and debris inside a small, warm, wet drain, or a trap that has dried out. Pouring hot water or bleach down it rarely clears the film. Manufacturers say to scrub dispenser drains daily and clean ice bin drains about every three months.
What makes a soda or ice drain smell?
Three things, and a smelly drain is often more than one.
A slime film on the pipe wall. Hoshizaki's ice machine manual puts it plainly: "In some conditions, slime may build up inside the ice storage bin drain and prevent water from draining properly." Beverage drains see the same thing from spilled syrup and carbonated water. Ohio State University's drain fly fact sheet describes the stuff as "bacterial muck, slime or gelatinous film often accumulating on the sides of drains," and says larvae "feed on the decaying organic matter, bacterial films, algae and sediment" in it. That film is what you smell, and it is also what feeds drain flies around the soda station.
A slow or partly blocked drain. When the film thickens, water stops moving and sits. Hoshizaki warns that "If the ice storage bin drain becomes clogged, water could build up in the bin and overflow." Standing water that never gets flushed turns sour quickly, and a drain that backs up into the ice bin is a sanitation problem as well as a smell.
A dry or leaking trap. The drain below the soda station or ice machine usually ends at a trapped floor sink, standpipe or floor drain, and the trap's water seal is what blocks sewer odor. The 2024 International Plumbing Code says "Each fixture trap shall have a liquid seal of not less than 2 inches (51 mm) and not more than 4 inches (102 mm)," and that "trap seals subject to evaporation" must be protected, for example by a trap seal primer. A floor sink that gets only a small trickle of ice machine meltwater, or none overnight, can dry out and let sewer gas through. Phoenix did not amend those IPC sections, so the model code text applies. Our page on why dry floor drains smell like sewer in Arizona explains the evaporation problem, and trap primers for commercial floor drains covers the fix.
How to tell which one you have: a sour, syrupy or musty smell that sits right at the machine, often with small flies, points to film. A flat sewer smell that comes and goes, and may be worst after a quiet weekend, points to a dried trap or a vent problem. Our page on why a restaurant smells like sewer walks through the building-wide version.
Why doesn't hot water or bleach fix it?
Because the film is stuck to the pipe, and liquid runs past it. Ohio State's fact sheet says "The use of bleach does not seem to rid pipes of the scum, and the drain fly larvae are surprisingly resistant to bleach." It also says the effective approach is to remove the breeding material: "cleaning pipes and traps with a good, stiff, long-handled brush." And it warns against shortcuts: "There are no insecticides registered for use in drains or sewage systems, so do not simply pour an insecticide down a drain in the hopes that it will kill the larvae."
Hot water has a place after the scrubbing. The same fact sheet says that after mechanical cleaning you can "flush lines with boiling water" to remove leftovers, though in a commercial building with plastic or older pipe you should ask your plumber what the line can take. The cleaning is the scrubbing. The rinse is the rinse.
Some manufacturers do call for a sanitizer, and you should follow theirs over any general advice. Hoshizaki's drain procedure for its ice machines is to pour a sanitizing solution made from chlorine bleach, diluted to about 200 ppm, into the bin, then clean the liner with a neutral cleaner and rinse. It says to do it "once every 3 months or as often as necessary for conditions."
What should staff do every day, and every quarter?
Do what the equipment maker specifies. Two examples from manufacturer sources:
- Soda dispensers. Coca-Cola's Crew Connect sheet for its Freestyle dispensers says to "Follow this cleaning routine daily to prevent drain clogs." The routine is to sanitize the cup rest, drip tray and drain spider, and then "thoroughly scrub inside the dispenser drain" with the long drain brush before pouring the rest of the sanitizer slowly down the drain.
- Ice machines and bins. Hoshizaki's quarterly drain procedure above, plus its yearly full cleaning. If you have a different brand, find that manual and follow its interval and its chemical.
If the same drain keeps smelling after the brush and sanitizer, the film has moved past where a brush reaches. That is the point to call a plumber, not the point to add more chemicals.
What does a plumber do about it?
A plumber works on the part you can't reach: the small branch line between the fixture and the floor sink, or the lateral that carries it to the main. The usual sequence is a camera look, to see whether it is film, a low spot or a break, then cleaning the line with a small-diameter jetting hose, sometimes with a cleaning solution run through, then a flush. HQ Plumbing & Air does this for restaurants: we jet restaurant lateral lines from the inside with a small hose, and for smelly soda machine and ice well drains we use a cleaning solution, scheduled before opening or after close so the bar and kitchen are not disrupted. See what hydro jetting is for how the equipment works.
A couple of things to ask before any solution goes down a line:
- Which solution, and what does it do to the pipe and the downstream waste? Phoenix's FOG manual says "The use of chemicals, enzymes, proteins, bacteria, grease solvents, or emulsifiers to temporarily dissolve fats, oils, and grease is prohibited." That rule is written for grease interceptors, so ask whether your soda or ice drain ever reaches one, and keep any such product out of it.
- Where does the drain end? An ice machine drains through an air gap into a floor sink or standpipe, not straight into the sewer line. Hoshizaki's manual says "Drain line should not be piped directly to the sewer system," with a minimum 2-inch air gap. Our guide on how to drain a commercial ice machine legally covers the rule.
- Will the trap hold water afterward? The plumber should refill the trap and check that nothing is evaporating it.
For a fast sequence you can do yourself tonight: scrub and sanitize the dispenser drain, pour water into the floor sink to refill the trap, and write down the date. If the smell is back within a week or two, schedule the line cleaning. HQ gives free estimates and upfront pricing, and we are licensed and insured with 24/7 emergency service.