How Often Should an Oil Interceptor Be Emptied?

The short answer

There’s no single fixed timetable that fits every site. The Environment Agency’s guidance says British Standards recommend checking an oil separator at least every 6 months. It should be emptied whenever a significant amount of oil or silt has built up, after any oil spill, and whenever the alarm goes off. On top of that, the British Standard recommends an integrity test at least every 5 years.

A busy forecourt or wash bay may need emptying much more often than a quiet staff car park. The right interval for your site comes from regular checks and your maintenance records.

What an interceptor does

An oil interceptor (also called an oil separator) sits in your surface water drainage. Rainwater running off yards, car parks and forecourts carries oil and silt with it. The interceptor holds that water long enough for oil to float to the top and silt to settle at the bottom, so cleaner water leaves the outlet.

It can only hold so much. Once the oil layer or silt gets too deep, oil can pass straight through into the drains.

Which sites usually have one?

The government’s pollution prevention guidance says a separator is typically needed for sites with a risk of oil contamination, such as car parks larger than 800m² or with 50 or more spaces, vehicle maintenance areas, roads and refuelling facilities.

Suction hose lowered into an open oil interceptor chamber on a forecourt

What to check every 6 months

The guidance says to check how much oil and silt has built up, and that all the parts are working. Your separator manufacturer’s instructions will say exactly what to look at, for example the alarm, any coalescer and the closure device.

Signs it needs emptying now

The high-level alarm has gone off
There’s been an oil or fuel spill on the area that drains to it
Oil is visible at the outlet or in the chamber after it
Drains on the site are slow, or there’s a strong smell of fuel or oil
Nobody knows when it was last emptied

What affects how often

Size of the interceptor compared with the area it drains
Traffic and activity: fuel forecourts, HGV yards and workshops build up oil faster
Silt: yards with gravel, mud or plant movements fill with silt quickly
Wash bays: the guidance warns that separators don’t work properly if there’s detergent in the water, for example from car washing, so wash water may need a different solution

Alarms

Since 1 January 2021 it has been a legal requirement, under the Construction Products Regulations, for oil separators supplied in England, Wales and Scotland to have an automatic warning device or high-level alarm. Older units may not have one, which makes regular checks even more important.

After it’s emptied

The separator must be refilled with clean water before it goes back into use. The guidance says not to use the settled water taken out of it. Without clean water in it, the separator won’t hold oil if there’s a spill.

The waste is hazardous

The oil and sediment removed from an interceptor is hazardous waste. The guidance says it must be moved under a hazardous waste consignment note and taken to a permitted facility that can accept it. Use a waste removal company with experience of separators and a valid waste carrier registration. Keep a log of every inspection, emptying and repair.

Interceptor emptying with BL Oils

We empty interceptors at forecourts, car parks, wash bays, workshops and industrial sites across all of Yorkshire, Derbyshire, Nottinghamshire and Lincolnshire, and take the waste to a permitted facility with the correct paperwork. See interceptor waste. If you’re not sure when yours was last emptied, tell us when you ask for a quote. For garages and dealerships, we can collect waste oil and filters on the same visit.

Frequently asked questions

Is there a legal requirement to empty an oil interceptor?

There’s no single fixed interval in law, but you must not cause pollution. Guidance says to check separators at least every 6 months and empty them when significant oil or silt builds up, after a spill or when the alarm activates.

What happens if an interceptor isn’t emptied?

Once it’s full, oil can pass through into the drains and on to rivers or groundwater. Causing pollution can lead to an unlimited fine, prison, or both.

Is interceptor waste hazardous?

Yes. Oil and sediment removed from an interceptor is hazardous waste and must be moved under a hazardous waste consignment note to a permitted facility.

Does the interceptor need refilling after emptying?

Yes. It must be refilled with clean water, not the settled water taken out of it, before it goes back into use.

My interceptor alarm has gone off. What should I do?

Call us on 07785 921493. Our phone is answered 24/7. If oil has reached a drain or watercourse, also call the Environment Agency incident hotline on 0800 80 70 60.

Need waste oil collected? BL Oils is based in Doncaster and collects from businesses across all of Yorkshire, plus Derbyshire, Nottinghamshire and Lincolnshire. Call or WhatsApp 07785 921493, email info@bloils.co.uk or ask for a free quote. Got an urgent problem? Our phone is answered 24/7: see emergency waste oil collection.

Sources and further reading

Checked against official guidance in October 2026. This guide is general information for businesses in England, not legal advice. Rules change, so check the linked guidance or ask the Environment Agency if you’re unsure.