MySepticCheck

Seller guide · England

Selling a house with off-mains drainage

A practical guide to identifying your private drainage system and organising the information a buyer may need.

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What does off-mains drainage mean?

Off-mains drainage is private foul drainage that is not connected to a public foul sewer. A property may use a septic tank, a small sewage treatment plant or a cesspool. The system may serve one home or be shared with neighbouring properties.

Knowing which system you have matters because the operation, discharge arrangements and rules are not the same for every type.

Common types of private drainage

Septic tank Separates and partially treats sewage before liquid normally passes to a drainage field in the ground.
Sewage treatment plant Treats sewage before a qualifying discharge to the ground or surface water, subject to the applicable rules.
Cesspool A sealed holding tank with no discharge. It stores sewage and needs regular emptying by a registered waste carrier.

Information to gather before selling

A buyer, conveyancer or surveyor may ask for:

  • the type, approximate age and location of the system
  • whether it serves only your property or is shared
  • where a septic tank or treatment plant discharges
  • any permit, installation or alteration information you hold
  • emptying, servicing, maintenance and repair records
  • plans, photographs, manuals and guarantees, where available
  • access arrangements and relevant rights for shared or off-site equipment

Do not worry if some records are missing. Identifying the gaps early gives you time to investigate them before conveyancing is under pressure.

A sensible order for getting sale-ready

  1. Confirm whether the property is connected to the public foul sewer.
  2. Identify the private drainage system and who is responsible for it.
  3. Locate the tank or plant, pipework, drainage field and discharge point where relevant.
  4. Gather the records and written information you already have.
  5. Check unclear arrangements with a suitable drainage professional or your conveyancer.
  6. Provide the buyer with the required information about the system.

Organise your off-mains drainage information

MySepticCheck brings your system details, maintenance history, discharge information and supporting evidence into one organised seller record. It then highlights information gaps using a Green, Amber or Red readiness result.

Start my property check Identify my drainage system Read the septic tank guide

Official guidance

Read the Environment Agency's guidance for septic tanks and sewage treatment plants. GOV.UK provides separate guidance for cesspools.

Guidance reviewed 4 September 2026. This page is for properties in England. MySepticCheck is an information and readiness tool, not a compliance certificate, survey, physical inspection or legal or environmental advice.