Blocked sewage drains are a right mess. They stink, they’re hazardous, and if you ignore them, you’re looking at structural damage, health risks, and a hefty repair bill. Whether you’re a homeowner, facilities manager, or in construction, I’ll guide you through spotting a blockage, sorting it out yourself, knowing when to call the pros, and keeping things legal under UK law.
We’ve seen how dodgy drainage or wrong assumptions about underground pipes can turn small issues into nightmares. This guide isn’t just theory, it’s built on our real-world experience and specialist know-how from underground utility surveys. Let’s dive in.
How Do You Know If a Sewage Drain Is Blocked?
Key Signs of a Blocked Drain
Spotting a blockage early saves you a world of trouble. Look out for these telltale signs:
- Gurgling noises from sinks or toilets when you flush or drain water.
- Water drains slowly from basins, baths, or showers.
- Foul odours wafting from drains or manholes.
- Toilets with water levels rising higher than usual after flushing.
- Localised flooding, especially around sewer inspection chambers or storm water drains
Common Causes of Sewage Blockages
Blockages don’t just happen, they’re caused. Here’s what’s usually to blame:
- Fat, oil, and grease (FOG) build-up.
- Wet wipes, sanitary products, or other non-flushables clogging the pipes.
- Tree roots sneaking into pipe joints, especially in older systems.
- Collapsed or misaligned pipework, often due to age or ground movement over time
- Poor drainage design, like pipes with insufficient slope to keep things flowing.
- Poor construction, like broken pipes being without being fixed, or building debris allowed to enter
DIY Methods to Try Before Calling a Pro
You don’t always need to call out the cavalry. Here are three safe, effective DIY methods to try first. But don’t go in blind. Check the safety precautions below.
Safety Precautions for DIY Drain Unblocking
Before you start, protect yourself and your property:
- Wear gloves, eye protection, and old clothes. Sewage is nasty.
- Ventilate the area to avoid breathing in bacteria.
- Keep kids and pets well away from open drains or manholes.
- Never mix chemical cleaners, as they can release toxic gases.
1. Boiling Water + Detergent
Perfect for grease-related blockages in kitchen pipes.
- Boil a kettle of water and add a squirt of washing-up liquid.
- Pour slowly down the drain to break up grease, avoiding splashes.
- Repeat two or three times, waiting a few minutes between pours.
- Flush with cold water to check if the drain’s flowing freely.
2. Plungers and Drain Rods
These are your go-to tools for stubborn blockages.
- Rubber Plunger: Use for internal blockages in sinks or toilets. Create a tight seal and pump vigorously to shift the clog.
- Drain Rods: For external drains or manholes, use rods with a plunger or screw head. Insert into the drain and rotate clockwise to avoid unscrewing the rods while inside the pipe system. Once you hit the area of resistance, ram it to see if you can break through.
- Always clean tools thoroughly after use to avoid contamination.
3. Drain Unblocker Chemicals
Chemical cleaners can work for certain types of blockages, but they’re not a magic fix.
- Choose a product designed for drains (check the label for sewage compatibility).
- Wear full PPE: gloves, goggles, and a mask etc. to avoid burns or fumes.
- Follow instructions exactly, and never mix chemicals to prevent toxic reactions.
- Avoid using on fully blocked or external pipes, as they’re less effective and can damage pipework.
When to Call in the Professionals
Some blockages are too big for DIY. Here’s when to pick up the phone.
Indicators That You Need Expert Help
Call a drainage specialist if you notice:
- Sewage overflowing from external drains or manholes.
- Multiple fixtures (sinks, toilets, showers) blocked across the property.
- Suspected structural issues, like cracks in pipes or tree root ingress.
- Persistent sulphurous smells that don’t clear with DIY efforts.
- Sewage backing up into your home – act fast to avoid health risks.
Tools and Techniques Used by Drainage Specialists
Professionals have the gear to tackle serious blockages:
- CCTV Drainage Surveys: Cameras snake through pipes to pinpoint blockages or damage.
- High-Pressure Water Jetting: Blasts away grease and debris.
- Root Cutting and Descaling: Special tools remove tough obstructions.
- Excavation and Repair: For broken pipes, pros dig up and replace damaged sections.
The Role of Underground Utility Surveys
Before any digging starts, you need to know what’s underground to reduce the possibility of an accidental strike on a utility! That’s where we at Terrain Surveys come in.
Locating buried utilities and infrastructure is our specialism! Highly trained and experienced surveyors using Electromagnetic Locators (EML) and Ground Penetrating Radar (GPR) can pinpoint sub-surface features so you can break-ground with confidence.
When it comes to mapping & investigating underground drainage – a CCTV drainage survey is a must! We use CCTV camera equipped rods and robots to map drainage assets accurately and to identify issues. You’ll know the full condition of the entire pipe network, and the exact cause and location of any defects, so you can take the required action.
We can even clear certain types of issues during the inspection as our engineers have vans equipped with high pressure water jetting (HPWJ) systems. For anything more complex, we’ll advise on what needs to be done, and we can recommend local tradesmen who will be able to carry out remediations.
Once we’ve identified the location of a problem, if it will require excavation, we can use GPR (ground penetrating radar) and EML (electromagnetic location) to check for other buried services (gas, electricity, phone, internet, other pipes etc). This information can be used to avoid accidentally striking buried infrastructure – which is both dangerous and costly!!
Cost Considerations for Professional Drainage Services
For a small domestic job you should expect:
- CCTV Surveys: £150–£500
- High-Pressure Jetting: £80–£200
- Excavation and Repairs: £500–£2,000+, especially for pipe replacements.
For commercial jobs, which tend to have more complex pipe networks, costs would start from £1000 for the CCTV survey.
Terrain Surveys specialise in commercial drainage condition & connectivity surveys. We frequently carry out surveys on historic sites, commercial buildings, building developments, and even the public sewers. Get in touch with us if you need a survey for a larger, or complex drainage network.
Who’s Responsible for a Blocked Drain?
Legal Responsibilities in the UK
Figuring out who’s on the hook for a blocked drain depends on where it is:
- Private Drains: If the blockage is within your property’s boundary and only affects your drains, you’re responsible. This includes pipes from your home to the boundary.
- Shared Drains: In flats or shared properties, responsibility may be split between residents or managed by the landlord or housing association.
- Public Sewers: If the issue is beyond your boundary in a public sewer, your water and sewage company takes over. Since 2011, most shared drains and lateral drains connected to public sewers are maintained by water companies under the Water Industry Act. However, some drains may be the responsibility of the local authority.
Unsure where your drain ends? Check your property’s drainage plans or contact your water company. You can find your provider at Water UK.
What to Do If You Think It’s a Public Sewer
If you suspect a public sewer issue:
- Contact your water company (e.g., Thames Water, Yorkshire Water) immediately.
- Provide the exact location, symptoms (e.g., flooding, smells), and any photos.
- They’ll inspect free of charge and clear the blockage if it’s their responsibility.
- Find contact details via Water UK.
How to Prevent Future Blockages
Keep your drains flowing with these simple habits.
1. Follow the 3 Ps Rule
Only flush:
- Pee
- Poo
- Toilet Paper
Bin wipes, sanitary products, cotton buds, and anything else. Even “flushable” wipes can clog pipes.
2. Use Sink Strainers and Grease Traps
Stop trouble before it starts:
- Fit sink strainers to catch food scraps and debris.
- Install grease traps in kitchens to collect fats and oils.
- Scrape plates into the bin, not the sink, before washing.
3. Regular Drain Maintenance
An ounce of prevention beats a ton of cure:
- Book 2-yearly CCTV inspections to catch issues early.
- Schedule high-pressure jetting every 2 years, to clear minor build-ups.
- Inspect pipe routes near trees for root intrusion.
For maintenance tips, check out The Environment Agency’s standards for sustainable drainage systems.
Conclusion
A blocked sewer or drainage run is a headache, but you’ve got options:
For small domestic blockages, start with DIY methods like boiling water or plungers for minor clogs. If things look grim (overflows, smells, or backups) call in a local plumber.
For larger, or more complex pipe systems, such as those serving multiple residential dwellings, or very old sewer systems connected to historic buildings, or pipe networks associated with commercial buildings, contact Terrain Surveys.
