Grease trap or grease separator? How to keep the drain clear

A grease separator is a tank or pit that sits between the kitchen drain and the sewer. The wastewater flows in and settles briefly. Because grease and oil are lighter than water, they float to the top and remain in the tank. Heavy particles, such as food scraps and sand, sink to the bottom; for this a grease separator often has a separate sludge trap. The cleaned water flows out from the bottom to the sewer. Colloquially, people also speak of a grease trap or grease catcher.

Who has a grease trap?

• Catering: restaurants, snack bars, cafeterias, hotels and caterers with a commercial kitchen.
• Other businesses where a lot of grease is produced in the kitchen, such as bakeries, butchers, canteens and care institutions.
• Some properties, especially older buildings or properties that previously housed a business. Sometimes the current occupant does not even know that there is a grease trap in the garden or cellar.

Many municipalities impose requirements on businesses that discharge grease-containing wastewater, for example regarding having a grease trap and its maintenance. Which rules apply to your situation varies per municipality and per type of business. Therefore, check with your municipality or environmental service what is expected of you.

Why does a grease trap need to be emptied?

The layer of grease in the tank grows with every day the kitchen is in use. At some point the tank is so full that there is no room left to separate grease. Then one of these things happens:

• The grease flows into the pipe behind it and the sewer, and deposits there. This leads to blockages that are harder to clear than a full tank.
• The tank itself becomes blocked and the water no longer flows through, causing the drains in the kitchen to back up.
• The grease and food waste start to rot. This produces a strong, unpleasant smell.

How often emptying is needed depends on the size of the grease trap and how much grease is produced in your kitchen. A busy restaurant has a different schedule than a small canteen. A specialist company can advise you on a suitable schedule.

Signs that the grease trap is full

• Bad smell in the kitchen, near the manhole cover or outside at the trap, often a rancid or sewage-like odour.
• Slow drainage from sinks, dishwasher or floor drains in the kitchen.
• Gurgling sounds in the drain.
• Water or grease coming up in a floor drain or from the lid of the grease trap.
• It's been a long time since the grease trap was emptied, or no one knows when it was last done.

Step-by-step plan for problems

1. Limit use of the drain. Stop rinsing if possible and don't run the dishwasher for now, to prevent overflow.
2. Check when the grease separator was last emptied. Look at your maintenance records or receipts from the emptying company.
3. Have the grease trap emptied. If it is full or it has been a long time, call in a specialist company that empties and cleans grease traps.
4. Then check the drain. If it still doesn't drain properly after emptying, there is probably grease or dirt in the pipes before or after the grease trap.
5. Have the pipes cleared. Then you can call us. We clear the drain pipes and sewer and can use a camera if necessary to see where the blockage is.

What PandFix does and doesn't do

We don't do the periodic emptying and cleaning of the grease separator itself; that's for specialist companies with suction tankers and proper disposal of grease waste. What we do: unblock the drain pipes in the kitchen, the connection to the grease separator and the pipe and sewer behind it. If a blockage keeps returning, we can use a camera inspection to see if there's grease build-up, subsidence or damage in the pipe. For business customers, read more on our business page.

What you'd better not do

• Don't pour chemical drain unblockers or enzymes into the grease separator without advice. Products that dissolve grease can cause the grease to settle further down the pipe, where it blocks again.
• Do not flush large quantities of hot water to get rid of the grease. The grease cools further down and solidifies there.
• Do not open the lid yourself and do not dispose of the contents yourself. Harmful gases can be released and grease waste does not belong with ordinary waste or in the sewer.
• Do not bypass the grease trap by connecting drains directly to the sewer.

Where is the grease separator located?

A grease separator is usually located in the ground outside the building, in a cellar or crawl space, or as a separate tank in or near the kitchen. Recognisable features are one or more manhole covers and sometimes a separate opening for emptying. If you don't know where it is, check the building plans or ask the previous user or the emptying company.

How to prevent problems

• Have the grease separator emptied according to a fixed schedule and keep a record of when it happens.
• Collect deep-frying fat and oil separately and have it collected; never pour it down the kitchen sink.
• Scrape pans and plates into the bin before rinsing them.
• Use strainers in sinks and floor drains.
• Instruct new staff about what may and may not go down the drain.

If it's a normal kitchen drain at home, read kitchen drain or sink blocked. If you smell a sewer odour in the property without a clear cause, see sewer smell in the house. More about our approach can be found on the drain unblocking page.

Costs: what can you expect?

With a grease trap or grease separator, two types of work overlap: emptying the trap and unblocking the pipes before or after it. For businesses, emptying is usually done with a suction tanker from a specialist company; that's a separate service. We mainly help when the drain to or from the trap is blocked, when there's odour nuisance or when an old grease trap in a home causes problems.

For a property with an old grease pit, we first inspect with a camera how the pipes before and after it run. Sometimes the pit has become redundant and can be bypassed; sometimes it needs to be cleaned and remains in use.

Do you run a catering establishment? Then schedule the emptying and flushing of the pipes at fixed times. A blockage during opening hours usually costs more than the maintenance itself.