Is It Actually the Drains?

The strongest sign

Rats Inside and No Way In Outside

If you have rats in the building and a careful look round the outside finds no entry point — sound brickwork, intact airbricks, no gaps at pipe entries, a closed roofline — that is the single best indicator that they are arriving from underneath.

The reason it is such a strong sign is that rats do not tunnel in from open ground for no reason when easier routes exist. If nothing easy exists above ground and they are still inside, the route is below it.

Worth being honest about the limits of "a careful look". The gaps that get missed are behind bin stores, under decking, where a service pipe enters low down, behind a downpipe, and under a garage door seal. Look at those specifically before concluding.

Where the noise is

Under You, Not Above You

Drain rats arrive at floor level and below it. So the noise is underfoot: running and scratching beneath a suspended floor, in a cellar, under stairs, behind a kitchen plinth.

Rats that came in at roof level or climbed give you noise overhead, in a loft or at first-floor ceiling level. Same animal, completely different job, and a blocker does nothing for the second one.

A useful check: where do the droppings start? Drain-fed activity concentrates near where pipework enters the building — under the sink, in the utility room, by the soil stack, in a basement — and spreads from there. Activity that is heaviest upstairs or in the loft did not come from the drain.

The smells

Two Different Ones

A sharp, ammonia-like smell is rat urine, and it builds where activity is concentrated and enclosed. It does not tell you where they came from, only that there are enough of them for long enough.

A drain smell that has appeared and stayed is more interesting. Foul air reaching the house means the water seal that should be stopping it has been bypassed — a dry trap, a damaged trap, a broken pipe under the floor, or a defective interceptor. Every one of those is also a way in. A new and persistent drain smell with rats is a strong combination.

Do not chase a drain smell with bleach and air freshener. It is telling you something.

The history

Sudden, and With No Obvious Cause

Ordinary rat problems usually have a story: a neighbour's building work, a new compost heap, chickens, a bird feeder, a disturbed burrow, a run of bins. Ask around and something turns up.

Drain problems often have no story at all. The property is clean, nothing has changed outside, nothing has been disturbed, and rats have simply appeared indoors. That absence of an explanation is itself evidence.

The other historical tell is repeat treatment that has not ended it. Where a property has been baited more than once, gone quiet, and come back, the route is open and being resupplied. The sewer population is effectively unlimited, so baiting alone is a treadmill.

What settles it

Looking in the Chamber

Most of the above is inference. The thing that settles it is opening the inspection chamber and looking.

What a technician is looking for: rat droppings on the benching above water level, smears on the chamber wall, an open or displaced connection, a branch that does not go where it should, and whether the interceptor trap (if there is one) is intact. Droppings on dry benching are close to conclusive.

Where the chamber tells you nothing and the signs still point downwards, a camera goes further than a torch. That is the next step rather than the first one, and it is covered in the CCTV drain survey.

You can lift a chamber cover yourself if it lifts easily — they are heavy, so use two hands and keep fingers clear of the rebate. If it is sealed, bolted or under something, leave it.

Images on this page are illustrations only.

Short answers

Drain Blocker Questions

Going further

Drain and Rat Guides