Drainage – Ask Anything, Get Answers
Impartial, plain-English guidance on drains, soakaways, surveys, septic tanks, regulations, and more.
What is "drainage" in a household context?
"Drainage" describes the systems that collect and carry wastewater and surface water away from a property. For homes connected to the mains, this is typically a network of underground pipes leading to the public sewer. For properties off-mains, drainage includes septic tanks, drainage fields (soakaways), and compact sewage treatment plants. Good drainage protects living spaces, garden areas, and nearby watercourses.
Common drainage issues (and what they usually mean)
- Slow draining fixtures / gurgling: often partial blockage or ventilation issues.
- Smells indoors or outdoors: trapped waste, dry traps, or failing components.
- Frequent blockages: accumulated grease, wipes, or tree root ingress.
- Ground remains wet or boggy: possible drainage field overload or pipe leaks.
- Localised dips / cracking: potential sub-soil wash-out or broken/voided pipe runs.
If you're unsure where to start, open the chat and describe the symptoms. You'll get a concise plan of action.
How drainage problems are investigated
For recurring or unclear issues, a CCTV drain survey gives a visual record of pipe condition, location, and defects (e.g., cracks, displaced joints, roots, or collapse). For off-mains systems, site checks may include inspecting chambers, verifying septic tank baffles, and confirming whether a soakaway or drainage field is functioning as designed.
What a CCTV survey typically includes
- Clean/jet to remove debris so defects can be seen.
- Camera inspection with video stills and condition coding.
- Drain map (where feasible) to confirm routes and connections.
- Clear recommendations (no-dig lining, excavation, or monitoring).
On-mains vs off-mains: what's the difference?
On-mains drainage means your pipework connects to a public sewer. Repairs tend to involve unblocking, jetting, lining, or—if necessary—local excavation. Off-mains drainage means your property treats and disperses wastewater on site, usually via a septic tank plus drainage field, or a small sewage treatment plant.
Off-mains components at a glance
- Septic tank: settles solids; clarified effluent goes to a properly designed drainage field.
- Drainage field (soakaway): disperses treated effluent into soil (requires a percolation test to size).
- Sewage treatment plant: treats to a higher standard; discharge routes must comply with current rules.
Repairs & methods (plain-English overview)
- Jetting & mechanical clearing: first-line unblocking for fats, silt, and loose debris.
- No-dig patch/lining: creates a new inner pipe skin to seal cracks and joints.
- Targeted excavation: used when the pipe has collapsed or misalignment is too severe for lining.
- Off-mains fixes: can include tank component replacement (e.g., baffles), drainage field redesign, or plant servicing.
Compliance & permissions (high-level)
Some works—especially new off-mains systems or discharges—require permissions and must meet current rules. Building Control may ask for a percolation test and design notes for drainage fields. Discharges must follow current standards; where direct outfalls to ditches were once common, today they often are not permitted without compliant treatment and consent.
Before undertaking works
- Document the problem (photos/survey extracts).
- Check if approvals/permits are needed.
- Keep reports and receipts—useful for insurance or property sale.
FAQs
Do I need a survey before selling a house?
Many buyers (and their lenders/insurers) now expect drainage evidence. A survey can prevent surprises and clarify any responsibilities for shared or private sections.
Who is responsible for drains?
As a rule of thumb, drains within your boundary serving only your home are your responsibility; shared lateral sections may be the water company's. Local variations apply—ask in chat for a quick sense-check.
Can drains cause subsidence?
Yes. Leaking pipework can wash away fine soils around foundations. Prolonged leakage may increase movement risk. Evidence tends to involve surveys, boreholes, or long-term monitoring.
What is a percolation test?
A timed soil infiltration test used to size a drainage field correctly. Building Control will typically expect to see the result and design calcs for a new installation or major replacement.