How often should an interceptor be emptied?

What the guidance says

The Environment Agency's guidance for oil separators was PPG 3, now reissued as GPP 3 (Guidance for Pollution Prevention: use and design of oil separators). It is guidance, not law, and it points the same way as manufacturers and EN-type maintenance guidance: regular checks of oil and silt levels, servicing commonly recommended at least annually, and emptying when accumulated oil and silt reduce the separator's capacity to do its job. No statute sets an emptying interval, and any contractor who claims "the law says every six months" is selling, not citing.

What most sites actually do

• Forecourts and busy depots commonly service more often, because silt and oil arrive faster; many run six-monthly or annual scheduled visits.
• Car parks and quieter yards often find an annual service with checks in between keeps the tank within capacity.
• Sites with alarms: automatic oil-level alarms (commonly fitted on separators) turn the schedule into a prompt, empty when the alarm or the dipping says so, not by the calendar alone.
• Every site: keep the paperwork. Consignment notes from each empty are your evidence the waste went where it should; see the regulations guide.

Signs a tank is overdue

1. Sheen or oil in the discharge, or downstream drains smelling of fuel: the separator is passing what it should be catching.
2. Standing water or slow drainage on the forecourt or car park after rain: silt is stealing the tank's working volume.
3. Nobody on site can say when it was last emptied: with no records, book an empty and start the record there.

Waiting for a pollution incident costs more than any servicing schedule: cleanup, and potential enforcement, sit with the site operator. A scheduled service at £300–£800 per visit (typical 2026 quotes) is the cheap version of this story. Get quotes for a schedule that fits your site.