Treat it as a health hazard first
When wastewater backs up out of a drain, a toilet, or a floor drain, the first job isn't plumbing — it's keeping people away from contaminated water. Sewage carries bacteria and pathogens, so get children and pets out of the affected area, keep bare skin and food away from it, and don't run more water down any drain in the apartment until you understand the blockage. Every flush, every sink, every shower upstream adds to what's coming back up.
Open windows for ventilation and switch off electricity to the affected area if water is anywhere near outlets, cords, or appliances — the same water-and-electricity rule that governs any flood. Don't try to bail or push sewage around the apartment with a regular mop and bucket you'll reuse; if you must contain it, use gloves, and treat everything that touches it as contaminated. The goal in the first few minutes is simple: stop adding water, and keep the contamination contained.
If the backup is widespread or recurring, or if it's pushing up through multiple fixtures at once, that pattern points past your apartment and toward a shared line — which changes who you call and who pays. But the health steps come first regardless of whose blockage it turns out to be. A safe, ventilated, water-off apartment is the right starting point for every version of this problem.
Your line, the building's line, or the city's main?
The clearest diagnostic is how many fixtures are affected. If just one sink or one toilet backs up while everything else drains normally, the blockage is almost certainly local to that fixture or its branch — your problem to clear. If several fixtures back up together, or if flushing a toilet makes the tub gurgle and rise, the clog is downstream where the lines join, which in an apartment building usually means a shared stack or the building's house drain — the owner's responsibility.
In a building, the lines from individual apartments feed into vertical stacks and then into the building's main house drain, which connects to the city sewer at the street. A backup in the lowest fixtures of the building — a basement floor drain, a ground-floor unit — when upper floors are fine often means the blockage sits in that house drain or where it meets the city line. That's building territory, escalating toward city territory, not a single tenant's clog.
The city's sewer main runs under the street, and the connection from the building to that main is generally the building owner's responsibility up to the city line. A true city-main problem usually isn't one building's backup — it's water surfacing in the street, multiple buildings affected, or sewage backing up across a block. If you suspect the public sewer, that's where NYC DEP comes in, and it's a call alongside the plumber, not instead of one.
What NYC DEP does — and doesn't
The New York City Department of Environmental Protection runs the public sewer system — the mains under the streets. If the problem is a blocked or surcharged public sewer, DEP is the agency that investigates and works on the city's side of the line. You reach them through 311, which routes sewer complaints to DEP; report it when water is backing up across multiple buildings, surfacing in the street, or when you have reason to believe the public main is the cause rather than your building's plumbing.
What DEP does not do is clear the blockage inside your building or your apartment. The building's house drain, its stacks, your branch lines, and your fixtures are private plumbing — DEP's responsibility starts at the city main, not at your toilet. So a backup almost always means two separate questions: is the city main involved (DEP and 311), and what's clogged on the private side (a plumber). In a serious backup you pursue both at once rather than waiting to see which it is.
Reporting to 311 also creates an official record, which matters if the cause turns out to be the public sewer — that record is what supports a claim and what pressures the city to act. But don't let a 311 ticket stall your private repair: if sewage is in your apartment and the building's line is the cause, the building needs a plumber moving now, regardless of what DEP eventually finds at the street.
What a plumber actually does
A licensed plumber's first move on a serious or repeat backup is usually a camera — a waterproof video line snaked into the drain to see exactly what and where the blockage is. That's how you separate a clog from a collapsed pipe, find tree roots that have invaded an old clay house drain, or locate where in the run the problem sits. Camera first means the repair is aimed, not guessed, and it tells you whether you're clearing a blockage or facing a damaged pipe.
For clearing, the two main tools are the snake (a motorized auger that breaks through and pulls back clogs) and the hydro-jet (high-pressure water that scours the inside of the pipe). A snake punches through a specific blockage; a hydro-jet clears grease, scale, and root intrusion along a whole length of line and leaves the pipe walls clean. Which one fits depends on what the camera found — a single obstruction versus a line caked along its length — and on the age and condition of the pipe.
If the camera reveals a broken, collapsed, or root-shattered pipe rather than a simple clog, you're past clearing and into repair, which can mean excavation or pipe replacement and, in NYC, permits filed with the city. That's licensed work, and on a building's house drain or sewer connection it's exactly the kind of job where the LMP, the filing, and the inspection protect everyone. Ask the plumber to show you the camera footage — for a backup that keeps recurring, seeing the actual pipe is how you stop paying to clear the same clog twice.
Who pays for what
The rough rule follows responsibility. A clog confined to your own fixture or branch line — your kitchen sink, your toilet — is generally yours in a rental only if you caused it; building plumbing failures are the owner's. A backup in shared stacks or the building's house drain is the owner's repair and the owner's bill. And a confirmed public-sewer problem is the city's side of the line. The hard part is usually proving which it was, which is why the camera footage and the 311 record matter so much.
For tenants, the practical playbook is: make the apartment safe, report the backup to the super and management in writing immediately, and file with 311 if a shared or public line is in play. Don't unilaterally hire a plumber to work on the building's stack or house drain — that's the owner's equipment, access, and bill, and reimbursement is a fight most leases don't support. Your leverage is documentation and, for a building that won't act on a health hazard, an HPD complaint through 311.
When the repair is genuinely yours — you own the building, or it's your unit's own line in a condo or co-op per your bylaws — Reset shows which licensed plumbers can move now, with price bands and trip fees published before you book, every profile verified against the DOB roster. A sewage backup is a health hazard, so the Reset Guarantee applies: emergency requests are confirmed within 30 minutes, or Reset's in-house crew is dispatched automatically. Coverage is live across the Bronx, Manhattan, Brooklyn, and Queens, with Staten Island opening later in 2026.