Why does my condo smell like sewage when I come back after months away?

Because the water in one or more P-traps evaporated while the unit sat empty, and sewer gas from the building's stack has been drifting in through the open drain. Run every drain in the unit for thirty seconds, including showers, floor drains and the washing machine standpipe. If the smell is gone within a day, that was the cause.

How long does it take for a P-trap to dry out?

It depends on the fixture and the room, but a warm, closed Miami unit with the air-conditioning set high can dry a shallow trap in a few weeks. Guest bathrooms and floor drains are the usual first to go. A cup of mineral oil poured into the trap before you leave slows evaporation considerably.

Is sewer gas in an apartment dangerous?

At the concentration that reaches a room from a dry trap it is unpleasant rather than harmful, but it means a seal has failed and should be found. If a smell is strong, persistent, and does not respond to refilling traps, have the source located rather than living with it — and ventilate the unit in the meantime.

Can the air-conditioning cause a sewer smell?

Indirectly, yes. In many Miami buildings the AC condensate line drains into a plumbing fixture with its own trap. When the AC runs less — cooler months, or a unit set high while empty — that trap can dry out and vent sewer gas into the air handler closet, which the system then moves through the unit. Pouring water into that drain is the test.

Why does my drain gurgle when a neighbor flushes?

Gurgling after someone else's fixture drains means air is being pulled through your trap, which points at a venting problem in the shared stack — a blocked or undersized vent — rather than a clog in your unit. Report it to the association; it is the same issue that pulls traps dry.

Does a sewer smell mean my toilet wax ring has failed?

It can. A wax ring failure smells strongest at the base of the toilet, and the toilet often rocks slightly or the floor around it shows staining. If refilling all the traps in the unit does not clear the smell and it is concentrated at a toilet, the ring is the likely cause and the toilet needs to be reset with a new one.

Who pays for fixing a sewer smell in a Miami condo?

It depends on the source. Dry traps, wax rings, and drain piping inside the unit are the owner's responsibility under most Florida condo declarations; the shared stack and its roof vent are the association's. A plumber's job on this call is to identify which — and to document it — so the right party handles it.

Drains · 6 min read

Sewer Smell in a Miami Condo? Dry Traps, Empty Units and the Stack Vent

Most sewer smells in Miami condos come from a fixture nobody has used in months: a guest shower, a floor drain, a laundry standpipe. The water in its trap has evaporated and the stack is venting into the room. Here is how to find it, and what it means when refilling does not help.

By The God Plumber · Florida plumbers, in business since 2015 · Published September 22, 2026 · Updated September 22, 2026

A sewer smell in a Miami condo almost always comes from a dry P-trap — the U-shaped bend under a sink, shower, tub, floor drain or washing machine standpipe that is supposed to hold a plug of water. That water is the only thing between your unit and the building's drain stack. When a fixture goes unused for weeks, the water evaporates, the seal is gone, and sewer gas from the stack drifts into the room. The fix is to pour water down every drain that has not been used recently; if the smell fades within a day, that was it. If it does not, the cause is a failed toilet seal, an AC condensate line tied into a drain, or a problem with the building's vent stack — and that is where a plumber comes in.

Miami-Dade gets more of this than almost anywhere because so many units sit empty for part of the year. Seasonal owners in Aventura, Sunny Isles, Miami Beach, Brickell and Coral Gables lock up in spring and come back in the fall; second bathrooms in year-round homes go unused for months; a warm closed unit dries a trap faster than a cool one. Building managers know the pattern well — the first week of the season brings a wave of calls about a smell that turns out to be a guest bathroom.

Which drain is the dry one?

The one you forgot about. Go through the unit and run water into every drain for thirty seconds, in this order, because the culprits are usually the ones lowest on the list:

Guest bathroom shower, tub and sink — the most common source in a seasonal unit.
The washing machine standpipe behind the washer, especially if the unit has a laundry closet and the machine is rarely used.
Floor drains in a laundry closet, utility room, or balcony — many owners do not know they exist.
A wet bar, a second kitchen sink, or a bidet.
The air-conditioning condensate drain. In many Miami buildings the AC drip line ties into a plumbing drain with its own trap, and a dry trap there smells exactly like the others.

Sewer gas carries hydrogen sulfide and methane, which is why it smells the way it does. At the levels that reach a room from a dry trap it is a nuisance, not a hazard — but it is a sign that a seal has failed somewhere, and it is worth finding which one rather than masking it with an air freshener.

What if refilling the traps does not stop the smell?

Then the seal that failed is not a trap. Work through the following, roughly in order of likelihood:

Toilet wax ring. If the smell is strongest at the base of a toilet, or the toilet rocks even slightly, the seal between the toilet and the drain flange has failed. Water damage to the floor around the base often shows up at the same time. The toilet comes up, the ring is replaced, and the flange is checked.
A trap that empties itself. If one fixture goes dry within a week of being filled, the stack vent is not doing its job and the trap is being siphoned — usually when a large fixture upstairs drains. That is a building venting problem, not a unit problem.
A blocked or damaged vent stack. Every stack vents through the roof; a bird's nest, debris, or a rusted section on an older building lets pressure changes in the stack pull traps dry and push gas back through them. Gurgling drains after a neighbor flushes point the same way.
A cracked or disconnected drain fitting behind a wall. Rare, but on cast iron in pre-1975 Miami Beach and Coral Gables buildings, a corroded fitting can vent into the wall cavity.
A cleanout cap left loose after someone else's service call, or a missing cap on a stack cleanout in a utility closet.

Whose problem is it — mine or the building's?

In most Florida condominium declarations, the fixtures and the drain piping inside the unit are the owner's, and the shared stack and its roof vent are the association's. A dry trap, a wax ring, and a loose cleanout cap are yours. A trap that keeps siphoning dry, a blocked vent, or a smell that several units in the same column report at once belongs with the association and its plumber. The useful thing a plumber does on a call like this is separate the two clearly, so the owner is not paying to chase a building problem and the board has documentation when it is theirs. We photograph what we find and write down where, for exactly that reason.

How do I keep traps from drying out in an empty Miami unit?

Before you leave for the season, run every drain for a minute, then pour a cup of mineral oil into each trap. It floats on the water and slows evaporation for months.
Ask whoever checks the unit to run all the taps and flush the toilets once a month. It is the single most effective habit.
Close the toilet lids and shower doors; a closed fixture loses water more slowly.
Do not turn the water heater off at the breaker and leave it — that is fine, but do not shut the unit's main water valve if someone will be running the taps for you.
For fixtures nobody will ever use, a trap primer or a trap seal insert can be installed so the trap stays sealed without water.

If a smell in your Miami-Dade condo has outlasted a round of refilled traps, or you would like the unit checked before the season so there is nothing to find when you arrive, call the South Florida line at 954-594-1666 or book a visit at a time that suits you. We will find the seal that failed, tell you plainly whether it is yours or the building's, and put the price in writing before any work starts.