Seller guide · England
Selling a house with a sewage treatment plant
Organise the key system details, records and maintenance information before conveyancing begins.
What is a sewage treatment plant?
A sewage treatment plant is a private drainage system used by homes that are not connected to the public sewer. Unlike a septic tank, it treats sewage before the effluent is discharged to a suitable drainage field or, where the rules allow, surface water.
You may hear it called a package treatment plant, wastewater treatment plant or simply a treatment plant. It can be a compact unit, often with an electricity supply, pumps, alarms or mechanical parts that need regular servicing.
What should you tell the buyer when selling?
Environment Agency guidance for England says the seller must give the new operator written information about the sewage discharge when a property is sold. Gather and pass on the information you have about:
- the type, make and model of the treatment plant
- where the plant, drainage field or discharge point are located
- how the system discharges and whether it is shared
- changes or repairs made to the system
- the operating manual and maintenance instructions, where available
- servicing, emptying, repair and electricity records, where available
A clear written record helps the buyer understand what they are taking on and gives your conveyancer information to work with early.
Records worth gathering before you list
If you do not have every document, record what you do know and identify the gaps. Missing paperwork does not automatically stop a sale, but unanswered questions can slow it down.
Does a treatment plant need servicing?
Most treatment plants have manufacturer maintenance requirements. The manual should explain how often the plant needs servicing and desludging, plus any checks for pumps, blowers, filters, alarms or electrical controls.
Keep the manual and recent service records together. If the plant has an alarm, fault warning, unusual smell, poor drainage or uncertain condition, do not ignore it during a sale. A competent drainage professional may need to inspect the system.
Is a sewage treatment plant the same as a septic tank?
No. Both are forms of off-mains drainage, but they work differently. A septic tank mainly settles sewage and normally discharges to a drainage field. A sewage treatment plant provides further treatment before its discharge.
The distinction matters because the documents, maintenance needs and discharge arrangements may be different. If you are unsure which system you have, start with the system manual, service records or a drainage professional.
What about the General Binding Rules?
A small sewage treatment plant may need to meet the General Binding Rules or have an environmental permit. Which requirements apply depends on the discharge location, daily volume, system type, date of installation and whether the system has been changed.
Do not assume that a treatment plant is compliant simply because it is installed or has been regularly serviced. If you are unsure about the discharge route, permit, capacity or system condition, obtain appropriate professional or legal advice.
What if the treatment plant is shared?
If the plant serves more than one property, identify every connected property and gather documents about ownership, access, shared costs and maintenance responsibilities. A shared system may be on your land or a neighbour’s land.
Tell your conveyancer early if the arrangement is informal, access is unclear or there is a dispute. Do not describe an informal neighbour arrangement as a legally binding agreement.
A practical seller checklist
- Confirm the type, make and location of the treatment plant.
- Identify the discharge route and whether the system is shared.
- Find the operating manual, service reports and emptying records.
- Record alterations, repairs, alarms or known problems accurately.
- Gather plans, photographs, permits and warranty information if available.
- Give the relevant written information to the new operator.
- Raise unclear or missing information with your conveyancer early.
Organise your property information
MySepticCheck helps sellers in England bring their off-mains drainage details and supporting evidence into one organised Seller Information Pack. It highlights missing or unclear information before conveyancing progresses.
Official guidance
Read the Environment Agency’s guidance on small sewage discharges and the detailed General Binding Rules for discharges to the ground.
Guidance reviewed 16 September 2026. This page is for properties in England and provides general information only. MySepticCheck is an information and readiness tool, not a compliance certificate, survey, physical inspection or legal or environmental advice.