To rodent-proof drains, find the defect before you buy anything: clear any rats already inside, commission a CCTV drain survey to locate the cracked pipe, open joint, redundant branch or failed connection, then repair it and fit a rat blocker or seal where needed. The survey also shows whether the defect is on your private drain or the water company’s sewer, which decides who pays.
This guide is written for landlords, managing agents, block managers and commercial property and facilities managers. It covers how rats use drains, CCTV surveys, choosing between rat blockers, seals and repairs, installation checks, responsibility, tenant communication and record keeping. We have dealt with drain-related rat problems in London blocks of flats, restaurants, offices and rented homes since 2010.
Key takeaways
Drain proofing works when it is done in the right order. Skipping a step is the most common reason rats come back.
| Step | Why it matters | Who usually arranges it |
|---|---|---|
| 1. Clear active rats | Proofing first can trap rats inside the building | Pest controller |
| 2. CCTV drain survey | Finds the defect and shows whose pipe it is on | Pest controller or drainage contractor |
| 3. Repair the defect | The only permanent fix for cracked or displaced pipes | Drainage contractor, paid by the owner or water company |
| 4. Fit a rat blocker or seal | A backstop against sewer rats; caps redundant pipes | Pest controller or drainage contractor |
| 5. Inform tenants and keep records | Evidence for insurers, councils and disputes | Landlord or managing agent |
Table of Contents
- How rats get into drainage systems
- Why a CCTV drain survey matters before anything else
- Rat blockers, caps and repairs: choosing the right fix
- Installation practicalities and common pitfalls
- Planning, quotes and access in managed buildings
- Who is responsible, and what to do right now
- Keeping tenants informed and records straight
- How BioWise approaches drain-based rat problems
- Why the “just buy a blocker” advice misses the point
- How BioWise can help with drain proofing
- Sources
- FAQ
How rats get into drainage systems
Rats do not need much of a gap: BPCA advice is that they can get into a structure through a gap of about 15mm, roughly the width of a thumb. They swim confidently through partly flooded pipework and climb inside pipes, so drains give them a route into a building that is hidden, sheltered and close to food waste. A BPCA article on drainage inspections notes that a large majority of rat infestations in homes are estimated to start in the drains, which is why so many “mystery” infestations turn out to have nothing to do with the loft or the air bricks.
The defects that let this happen are almost always structural, not exotic:
- Cracked or fractured pipe sections, often from ground movement or old clay pipework
- Displaced or open joints where sections have shifted apart
- Uncapped or abandoned branch pipes left from old alterations or removed kitchens and bathrooms
- Failed or poorly fitted toilet pan connectors, a common route into the building itself
- Damaged inspection chamber covers, frames, benching or mortar around pipe entries
The signs are fairly consistent across properties: scratching behind walls or under floors at night, droppings near inspection chambers, a musky smell around drain covers, and blockages that keep coming back despite rodding. The one that gets tenants on the phone immediately, understandably, is a rat in a toilet bowl. For a homeowner’s view of the same problem, see our guide to rats in drains in the UK.
Why a CCTV drain survey matters before anything else
A drainage camera is fed through the pipe network and records what it finds: cracks, displaced joints, root ingress, open branches and failed connections. Before that, a pest controller can carry out a visual check of the inspection chambers, which often narrows down where to look. The footage and written report then matter for three practical reasons:
- Insurers, freeholders and clients need evidence, not a verbal opinion, before they authorise repair costs.
- Water companies need proof that a defect sits on the public sewer before they will act.
- Contractors need to see the actual pipe condition before recommending a blocker, a cap or a repair.
The survey also tells you something you cannot find out any other way: whether the defect is on a private drain or on a public sewer, which decides who pays. For managers with several properties, a survey usually costs less over time than repeat call-outs for a problem that keeps coming back because nobody found the hole.
Rat blockers, caps and repairs: choosing the right fix
Once the survey identifies the defect, the fix usually falls into one of three categories, and getting this choice right is the difference between a lasting solution and a short reprieve.
Rat blockers are one-way valves, usually stainless steel, fitted in an inspection chamber on the outgoing pipe. A flap opens under the flow of waste water leaving the property and closes at rest, so effluent still discharges normally but rats coming up from the sewer cannot get past. They are non-toxic and suit chambers with sound, round, accessible pipework.
Caps, bungs and grilles suit redundant branch pipes, disused inlets and vent terminals, where a valve is the wrong shape of solution. Redundant pipes should be properly capped or sealed off, and nothing should be fitted to a live pipe until a flow test confirms it is no longer in use.
Drain repairs and relining are the only permanent answer when the pipe itself is cracked, displaced or structurally compromised. A blocker fitted downstream of a fractured joint can stop sewer rats reaching it, but the joint is still failing and will keep letting water and roots in, and rats already living in the private drain can still use it.
| Fix | Best for | Limitations |
|---|---|---|
| Rat blocker (one-way valve) | Sound pipework where rats are coming up from the sewer | Not a repair; wipes and fat can jam it; needs regular checks |
| Cap, bung or grille | Redundant branches, disused inlets, vent terminals | Only for pipes confirmed as out of use, or for vents that must stay open |
| Repair or relining | Cracked, displaced or root-damaged pipes | Larger job, may need excavation; paid for by whoever owns the pipe |
Pro Tip: Do not treat a blocker as a substitute for a repair on a defect within your own boundary. It is a legitimate interim measure while a fix is scheduled, but leaving a cracked pipe unrepaired behind a valve just delays a bigger job.
The most durable outcome usually combines two of these: repair the structural fault, then fit a blocker as a backstop against rats arriving from further down the network. Physical exclusion also reduces reliance on rodenticides, which matters because resistance to anticoagulant baits is widespread in UK rats, and BPCA has highlighted that simple drain checks can reduce the need for rodenticides.
Installation practicalities and common pitfalls
A rat blocker needs specific conditions to work properly, and not every chamber offers them.
- Check the ownership first. If the chamber or pipe belongs to the water company, do not fit anything without its agreement.
- Check the pipe geometry. The device needs a round, undamaged pipe section with enough clearance for the flap to swing freely without catching on debris or roots.
- Expect some chambers to be unsuitable. Pipe condition, chamber size or a poor seating surface can rule out a standard blocker, in which case a repair or a different device is the fallback.
- Insist on a flow test after fitting. A blocker installed but never tested under real flow conditions has not been shown to work.
- Check the seating. A valve that does not sit flush against the pipe wall leaves a gap rats can exploit just as easily as before.
- Watch for wipes and fat. Both jam moving parts over time, so a blocker on a kitchen waste run needs more frequent checks than one on a domestic soil pipe.
- Schedule regular inspections, at least once a year and more often for commercial kitchens and food premises with heavy drain use.
Planning, quotes and access in managed buildings
We do not publish prices, because the cost of drain proofing depends almost entirely on what the survey finds. The table below shows what drives the scope of each type of work, so you can compare quotes on the same basis.
| Work | What it involves | What affects the scope |
|---|---|---|
| CCTV drain survey | Camera inspection with footage and a written report | Number of chambers, length of pipe runs, access |
| Rat blocker installation | Fitting, seating and flow testing a one-way valve | Chamber condition, pipe diameter, number of entry points |
| Minor joint or crack repair | Patch repair or a short liner at the defect | Depth, access, whether excavation is needed |
| Relining or section replacement | Lining or replacing longer runs of pipe | Pipe length, access, disruption to occupied areas |
In blocks and commercial buildings, access is often the hardest part. Inspection chambers may sit in shared courtyards, basements, car parks or tenants’ gardens, so give occupiers notice, arrange access to every chamber on the survey plan and, for restaurants and shops, book work around trading hours. Always ask for a written specification before work starts, covering the defect, the proposed fix, the device or materials and how the work will be tested.
Who is responsible, and what to do right now
CCTV footage settles the responsibility question quickly. As Ofwat explains, since 1 October 2011 most shared private sewers and lateral drains in England and Wales have been the responsibility of the water company, and the dividing line is usually the property boundary. Pipes that serve only one property and sit within its boundary remain the owner’s responsibility.
| Situation | Usually responsible |
|---|---|
| Drain serving only your property, within its boundary | The property owner |
| Shared sewer or lateral drain (mostly transferred in October 2011) | The water company |
| Rented home with a defective drain | The landlord, under the repairing duties for drains and the duty to keep the home fit to live in |
| Block of flats | Usually the freeholder or management company, as set out in the leases |
| Commercial premises | Depends on the repairing covenants in the lease |
| Blockages caused by misuse, such as fat or wipes | Can fall on the occupier; check the tenancy agreement or lease |
For most residential tenancies of under seven years, section 11 of the Landlord and Tenant Act 1985 requires the landlord to keep the structure and exterior in repair, expressly including drains, and the Homes (Fitness for Human Habitation) Act 2018 requires rented homes to be fit to live in, which covers pest problems. Separately, under the Prevention of Damage by Pests Act 1949 councils can serve notice on an owner or occupier requiring steps to deal with rats, including structural work, and can do the work themselves and recover the cost.
If rats are active now, work through these steps:
- Book a pest controller immediately if rats are already inside the building, to deal with the existing population safely.
- Commission the CCTV survey to locate the entry point and establish whose pipe the defect is on.
- Get a written repair specification covering the defect, the proposed fix and the materials.
- Report public sewer defects to the water company with the survey report, and consider an interim rat blocker on your side while you wait.
- Tell occupiers what is happening and what they can do to help.
- Keep the survey report, photos and invoices on file. Insurers, freeholders, councils and housing associations will all ask for this evidence if the problem comes back.
Keeping tenants informed and records straight
Drain work in occupied buildings goes more smoothly when tenants know what is happening. A short written notice explaining the problem, the planned survey or works, access dates and what to report helps avoid repeated complaints and missed appointments. Useful points to include:
- Keep toilet lids down and report any rat sightings, scratching or new droppings straight away.
- Do not pour fat, oil or grease down sinks, and bin wipes rather than flushing them, as both block drains and jam rat blockers.
- Keep bins closed and bin stores tidy, so rats that do reach the surface find nothing to eat.
- Leave inspection chamber covers alone and report any that are damaged or loose.
For commercial and multi-let buildings, keep a simple drain proofing record for each property: survey dates and reports, defects found, repairs and devices fitted, test results, inspection dates and any rat activity since. Our guide to pest management in housing associations covers the wider compliance picture for social landlords.
“When a rat problem comes back, the first thing a freeholder or insurer asks is what was done last time. A survey report, photos of the repair and a service report for every visit answer that in minutes. Without them, managers end up starting from scratch and often paying twice.”
– Matt Ochello, Sales Executive, BioWise
How BioWise approaches drain-based rat problems
Rats coming up through drains are one of the most common problems we deal with across London blocks, restaurants and rented homes. The sequence matters more than any single product.
“The sequence that works is never just fit a blocker and hope. We deal with the rats that are already in, survey the drain to find the real defect, get that defect repaired or sealed, then fit the right device and check it on a schedule. Skip a step and the rats find the gap you missed.”
– Ben, Service Technician, BioWise
We follow that sequence on single-property jobs and on ongoing contracts for restaurants, managing agents, housing providers and commercial portfolios. For a landlord or agent managing several addresses, a contract folds drain checks into the same visits as routine pest monitoring, which is easier to budget than reactive call-outs whenever a tenant reports scratching.
Why the “just buy a blocker” advice misses the point
Too much guidance online treats a rat blocker as a product you buy and fit yourself, like a draught excluder. That framing undersells the problem. A blocker fitted into a system with a cracked or displaced pipe treats the symptom while the actual defect keeps getting worse.
The conventional advice also overstates how widely blockers apply. Some chambers simply will not take a standard device properly, and nobody discovers that without a camera in the pipe first. Skipping the survey to save money on diagnosis is a common false economy, because it leads to devices fitted against the wrong defect.
What should change first is the order, not the budget. Property owners who commission a survey before buying anything usually buy the right fix once, rather than a blocker, then a repair, then a second blocker. Diagnosis first is the only way to know what you are actually fixing.
How BioWise can help with drain proofing
We give landlords, managing agents and facilities teams one accountable contractor for drain-related rat problems. Our BPCA-certified technicians deal with the active infestation, inspect the chambers, arrange a CCTV drain survey where a defect is suspected, fit rat blockers and caps, and coordinate repairs, with a written report at each stage that you can pass to freeholders, insurers or the water company.
See our rat control and facilities management pest control services. Our commercial pest control contracts include monthly visits with photo reports, digital service reports for audit files, emergency call-outs and unlimited minor pest proofing, and larger proofing projects are priced after a survey. For individual homes, our guide to rat proofing for London homes explains how we approach a whole-house survey.
BioWise is a family-run London company founded in 2010, a member of the BPCA and NPTA, CHAS accredited and SafeContractor approved, with same-day call-outs across every London borough and a 24/7 emergency response line. Call 0800 988 3568 or contact us online for a fixed written quote after a free survey.
BioWise Pest Control Maintenance
13 Hanover Square, London, W1S 1HN
Call 0800 988 3568 or email info@biowiseservices.com
Sources
- Drainage inspections for rodents – BPCA
- Rat control: how to get rid of and prevent rats – BPCA
- Responsibility for pipes and pumping stations – Ofwat
- Landlord and Tenant Act 1985, section 11 – legislation.gov.uk
FAQ
How can I stop rats coming up my drains?
Deal with any rats already inside, then commission a CCTV drain survey to find the defect. Repair cracked or displaced pipes, cap redundant branches and fit a one-way rat blocker where rats are coming up from the sewer. A blocker fitted without a survey often ends up in the wrong place or hides a defect that needs repairing.
Does a rat blocker stop rats for good?
Only if the drain behind it is sound. A blocker stops rats travelling up from the sewer, but it does not fix a cracked pipe or an open branch on your side, and wipes or fat can jam it. Fit it after the survey and any repairs, test it under flow and check it at least once a year.
Does bleach in drains deter rats?
No. Bleach has no meaningful deterrent effect on rats and does nothing about the structural defect letting them in. Pouring strong chemicals down drains can also harm the people using them and the drainage system itself. Relying on it instead of a proper survey just delays the real fix.
Who pays for drain repairs to stop rats?
Pipes serving only your property within its boundary are the owner’s responsibility; in rented homes that usually means the landlord. Most shared sewers and lateral drains have been the water company’s responsibility since October 2011. For blocks and commercial premises, check the lease. CCTV footage is the evidence that shows which applies.
Can rats come up through a toilet?
Yes. Rats can swim through the water trap, although it is uncommon and usually points to a drain defect or a failed toilet connection. Keep the lid down, keep children and pets out of the room and call a pest controller. A survey will show how the rat got in, and a repair or rat blocker stops it happening again.
