Rats In Drains: Why A Drain Survey Is Not A Rat Survey

This is one of the most common calls we take. The homeowner has done everything right, in the right order, and still has rats. The problem is rarely that the drainage company got it wrong. It is that a drain survey and a rodent ingress inspection are two completely different jobs, carried out by two different trades, looking for two different things.

Here is what we found on a job earlier this week, and what it tells you about how rats actually get into a house.

The Job: What The Drain Survey Missed

A homeowner called us after weeks of rodent activity. They had already paid a national drainage contractor for a CCTV survey. The report came back with no significant structural issue, so they assumed the drains were ruled out.

We never take a drain survey at face value until we have looked ourselves. Within two minutes of lifting the chamber cover, the picture was obvious.

Field note: what was actually in the chamber

• Fresh droppings sitting on the benching, directly below an open pipe. Rats leave droppings where they pause, not where they pass through, so this told us the chamber was being used as a route, not crossed by accident.
• Three redundant pipe stubs left completely open into the chamber. These are old connections from a previous bathroom, kitchen or downpipe that were abandoned during past building work and never sealed. They lead straight into the void under and alongside the property.
• Grease smears along the channel and around the pipe mouths. Rats have poor eyesight and run the same routes repeatedly, pressing their flanks against the same surfaces. The dirt and oil from their coats builds into dark, polished smears. Smearing this heavy means an established run, not a one-off visitor.
• Gnaw damage and a broken section of clay pipe, with soil and debris visible behind the break. That break is both an entry point and a slow collapse waiting to happen.
• Eroded benching where the concrete had worn away between the channel and the chamber wall, giving the rats somewhere to work at.

None of that is a fault a condition survey is designed to flag. Every bit of it is a rodent entry point.

The fix took a morning: all redundant stubs mortared and meshed, the benching made good, the defective section addressed, and three RatGate rodent blockers fitted to the live inlets.

The detail worth sitting with: this property had been dealing with rats on and off for five years. Five years of call-outs, bait, and activity that kept coming back, because nobody had closed the route in. One morning of proofing ended it.

Why Drains Are The Number One Route Into A UK Home

Rats are already in the sewer. That is the part most people miss. They are not tunnelling in from a field, they are living in a warm, wet, food-rich network that runs directly under the street and connects to every property on it.

The British Pest Control Association puts the figure at an estimated 80% of rat infestations originating from drainage issues (BPCA, drainage inspections for rodents). Our own experience across Cardiff and South Wales matches that closely. When we find a persistent rat problem that keeps coming back after baiting, the drains are the answer far more often than not.

Two local factors make South Wales particularly exposed:

Older salt-glazed clay drainage. Cardiff, Newport and the valleys towns carry a lot of Victorian and Edwardian terraced stock on original clay drainage. Clay is rigid and brittle. Ground movement, tree roots and a century of heavy vehicles above it produce cracked joints and fractured barrels, and those defects are exactly the size a rat needs.

Decades of extensions and conversions. Post-war and 1960s to 1980s estates across Barry, Caerphilly and the Vale have been extended, re-plumbed, conservatoried and loft-converted repeatedly. Every one of those jobs risks leaving a redundant pipe stub behind. Good builders cap them. Plenty do not, because an open stub causes no drainage problem at all. It only causes a pest problem.

Add to that a national picture of rising rodent pressure. A 2025 study in Science Advances analysing rodent data across 16 global cities found significant increases in 11 of them, linked to warming temperatures extending the active season and allowing extra breeding cycles (University of Richmond). Milder Welsh winters mean fewer natural pauses in breeding.

Drain Survey vs Rodent Ingress Inspection: What Each One Actually Covers

This is the heart of it. A CCTV drain survey is a genuinely valuable piece of work. It is just not the piece of work that finds rats.

Drainage surveys in the UK are coded to the WRc Manual of Drain and Sewer Condition Classification, a standard built to grade the structural and service condition of a pipe so that repairs can be prioritised and budgeted (WRc Group). It is an asset management standard. It was never designed to interpret rodent behaviour.

Both have their place. The point is that a clean drain survey report does not mean your drains are rat-proof. It means your pipes are structurally sound. Those are not the same statement.

If you are at that stage now, a rodent ingress inspection is usually a short visit and it either finds the route or rules the drains out properly.

The Five Defects We Check In Every Inspection Chamber

Lift a cover and you are looking at five things, in this order.

Warning Signs You Have Rats In Your Drains

Rats in the drainage system announce themselves differently from rats in a loft. Watch for:

• Activity that returns after treatment. Bait works, activity stops, then four weeks later it is back. That pattern almost always means an open route, not a failed treatment.
• Scratching from below floor level, in the kitchen, hallway or under a ground floor extension, rather than overhead.
• Droppings appearing in one fixed spot, often near a soil stack, boiler or under-sink pipework where services pass through the wall.
• Toilet water level dropping, or an unexplained smell of drains inside the property, which can point to a broken trap seal or a defective line.
• Rats seen in the garden near an inspection chamber, particularly at dusk.
• Nothing found in the loft. If a technician has proofed the roofline and the activity continues at ground level, the drains move to the top of the list.

There is a health reason to act rather than wait. Rat urine can carry the bacteria that cause leptospirosis, also known as Weil's disease, which is spread through contact with contaminated water or soil (NHS). Contaminated drainage and standing water in a chamber are exactly the conditions to take seriously, which is why chamber work is a job for someone with the right equipment and hygiene procedures.

How Rat Blockers Work, And What They Are Not

A rat blocker, sometimes called a non-return valve, is a one-way flap fitted inside a drain pipe. Waste water and solids push the flap open and flow out. A rat trying to travel the other way meets a flap it cannot lift or gnaw past. Fitted correctly, into a sound pipe, at the right point in the system, they are extremely effective. As Gareth puts it on site, best thing since sliced bread.

Two important caveats, and any honest pest professional will tell you both.

A blocker is a barrier, not a repair. The BPCA position is clear: a non-return valve works on the private section of drainage and should be treated as part of the solution, not the whole of it. If activity stops after fitting one, a CCTV survey should then be carried out to find and permanently fix the underlying defect.

Placement decides whether it works. A blocker fitted downstream of the actual breach does nothing at all, because the rats are already past it. This is why the evidence reading matters more than the product. Droppings, smears and gnaw marks tell you where the rats are entering, and that determines where the blocker goes.

What We Fitted On This Job: RatGate

The three blockers in the photographs are RatGate units, and they are what we fit as standard.

The reason is maintenance, which is where most non-return valves quietly fail. A typical blocker has to be pulled out before a drainage engineer can clear a blockage or run a camera down the line. In practice that means it gets removed for a jetting visit and, often enough, never goes back in. A blocker sitting in the back of a van protects nobody.

RatGate uses a patented liftable flap, UK Patent GB2588082, so the flap can be lifted, the line worked and the flap dropped back without the unit coming out. It is a small piece of design that decides whether the proofing is still working in three years.

The rest of the specification stacks up:

Stainless steel matters more than it might sound. A rat's incisors grow continuously and it will work at an obstruction it can smell food behind. Plastic gives eventually. Laser-cut 304L does not.

We fit them as part of a proofing job rather than sell them over the counter, so the honest position is this: the unit is only as good as the survey that decides where it goes. Fitted into the wrong pipe, it is an expensive piece of stainless steel. Fitted into the right one, after the stubs are sealed and the benching is made good, it closes the route for good.

The complete job is nearly always the same shape: read the evidence, seal every redundant stub with mortar and mesh, make good the benching and chamber walls, fit blockers to the live inlets, then repair the structural defect properly.

Prevention Checklist For Homeowners

You can do a meaningful amount of this yourself, safely, from above ground.

Do not climb into a chamber, do not put your hands into standing waste water, and do not attempt to bait a drain yourself. Rodenticides in drainage are covered by UK stewardship rules for good reason, and drain baiting done badly puts product into the water environment and at risk of reaching children, pets and wildlife.

Who Is Responsible For The Drain?

A frequent sticking point, and worth knowing before you pay for anything.

Since the 2011 private sewer transfer in England and Wales, most shared drains and lateral drains beyond the property boundary transferred to the water and sewerage companies. As a broad rule, the pipework inside your boundary that serves only your property remains your responsibility. Beyond the boundary, or where a pipe serves more than one property, it is usually the water company's. Your local water and sewerage provider can confirm ownership for a specific address (Defra guidance on the private sewers transfer regulations).

Separately, the Prevention of Damage by Pests Act 1949 places a duty on occupiers to notify the local authority in writing if they become aware of rats or mice on the land in substantial numbers, and gives local authorities the power to require treatment or structural works (legislation.gov.uk). If you are a landlord, this sits alongside your wider repair and habitation duties.

When To Call A Professional

Call us when any of the following is true:

• Rat activity has returned after a previous treatment
• You have had a drain survey that came back clear but the activity has not stopped
• You can see droppings, smears or gnaw marks in an inspection chamber
• You have recently had an extension, conservatory, new bathroom or kitchen and activity started afterwards
• Your property is a period terrace on original clay drainage
• You are a landlord, letting agent or food business with a compliance obligation

What a proper rodent ingress inspection gives you is not just a treatment. It is a written record of where the rats were entering, what was done about it, and proofing that closes the route rather than suppressing the symptom.

Key Takeaways

• An estimated 80% of rat infestations start with a drainage defect, not a hole in the roofline.
• A CCTV drain survey grades the condition of the pipe. It is not designed to identify rodent entry points, and a clear report does not mean your drains are rat-proof.
• Redundant open pipe stubs left in inspection chambers after building work are the most common single entry point we find.
• Droppings, grease smears and gnaw marks tell you where rats are entering, which is what determines where a rat blocker goes.
• Rat blockers are highly effective as part of a full proofing job, but they are a barrier, not a repair. The underlying defect still needs fixing.
• We fit RatGate stainless steel blockers, chosen for the liftable flap that lets drains be cleared without the unit being removed and never refitted.
• The property in this case study had been dealing with rats on and off for five years. The proofing took one morning.

Frequently Asked Questions