Why a treatment plant needs emptying
A sewage treatment plant, sometimes called a package treatment plant, treats waste water to a higher standard than a septic tank. It does this with air and bacteria. The solids it separates still collect as sludge in the bottom of the tank. If the sludge is left to build up, it is carried through with the treated water, the discharge becomes polluting, and the plant can fail.
Removing that sludge with a vacuum tanker is called emptying or desludging.
How often
The interval is set by the manufacturer and depends on the size of the plant and the number of people it serves. In England, the general binding rules for small sewage discharges require you to have the sludge removed by a registered waste carrier before it exceeds the plant's maximum capacity, and to maintain the plant as the manufacturer specifies. The government's guide to septic tanks and sewage treatment plants sets out what an owner must do.
What to tell the firm
- The make and model. For example Klargester BioDisc, Tricel, Marsh, Conder or WPL. The manual says how the plant should be emptied.
- The size, or how many people the plant was designed for.
- Access. How close a tanker can park, and whether the covers lift freely.
- When it was last emptied and serviced.
A plant should not usually be left empty. Many manufacturers say it must be refilled with clean water straight away, so ask the firm how they will leave it.
Who can do it
Sludge is controlled waste and must be taken away by a registered waste carrier. This register lists 275 companies. 275 of them held an in-date Environment Agency waste carrier registration when we last checked the register on 06 March 2026. Each listing shows the registration number and its expiry date.
Find a firm near you
Pick your region to see the registered companies that cover it, or use the form at the top of the page and we will pass your request on.