Reviewed by William "Willy" Vizcarrondo, NYS DEC Certified Commercial Pesticide Applicator C1825832. Updated September 23, 2026.
Short answer
Yes. UC IPM notes rats can enter buildings by swimming through sewers and coming up through toilets or broken drains, and Norway rats are strong swimmers. It's uncommon on Long Island, but it happens, usually where a drain line is broken or a floor drain has lost its water seal.
Through the pipe. A Norway rat in a sewer main or a building's drain line can swim the water-filled trap at the base of a toilet and surface in the bowl, and UC IPM lists swimming through sewers and entering through toilets or broken drains among the ways rats get into structures. It usually starts with a rat already in the sewer system under a street or a commercial block, and a house drain that connects to it, with a cracked or open line somewhere along the way. A rat surfacing in a bowl is a rat that was already traveling your plumbing.
Close the lid, put something heavy on it, and call. A rat in a toilet is frightened and wet and will try to get out, and a lidded bowl holds it. Flushing sometimes sends it back down; it doesn't fix why it came. The real question is where the sewer line is open. If you have a basement floor drain, a laundry sink or a shower drain without a trap seal, those are the other routes, and a house with a rat in the toilet needs its drain lines and floor drains checked, and a one-way flap valve on the main line is the permanent fix.
Most Long Island rat calls have nothing to do with plumbing. Norway rats burrow along foundations, under decks and behind bulkheads and come in at ground level through foundation gaps, unsealed utility lines and gaps under garage doors; UC IPM notes a young rat fits under a door with a half-inch gap. Roof rats, less common here, climb trees and wires to the roofline. If you're seeing droppings in the basement or hearing gnawing at night, the entry is almost certainly a foundation gap, not a toilet.
The toilet calls we get come from the denser, older sewered blocks in Nassau and the Queens and Bronx neighborhoods, where a house drain ties into an old street main and a rat population in the sewer has a route. In the canal-front South Shore towns, rats in the house almost always came from the bulkhead, not the plumbing. Either way, the drain lines and floor drains are the first thing we look at.
Related
Yes, if the drain has no trap seal or the trap has dried out. A basement floor drain or a laundry sink that hasn't been used in months can lose its water seal, and that's an open pipe. Running water into unused drains monthly keeps the seal, and a drain grate or flap valve stops anything larger.
A backflow or rat-flap valve on the main drain line, installed by a plumber, is the permanent fix, and any broken or cracked drain line gets repaired. Keeping floor drains sealed and used, and the basement free of food and pet food, takes away the reason to come up.
It can happen in older buildings where a rat population in the sewer or the building's drain stack has a route to the fixtures. It's a building problem, not a unit problem: the stack and the drain lines need to be checked and the entry closed, which is a landlord and plumber job with the pest work alongside it.
Still not sure? Call (516) 509-6001 and we'll tell you what you're dealing with.