Small Grease Trap: What You Gain, What You Give Up and When It Stops Working

It is Friday at 6.30pm. The pre-rinse at the sink has run since lunch, and the fryer basket has just come out. Under the bench by the dish area sits the trap, a metal box about the size of a small esky. Nobody has lifted its lid in months. Then the floor waste starts to gurgle.

That is the real problem with a small grease trap. It works well until the day it stops working, and those two days are not far apart.

This guide covers what "small" means in practice and what you give up by running one. It also gives you a simple rule for deciding whether to keep your trap, clean it more often or replace it.

What counts as a small grease trap

No single size makes a trap small. The word describes a trap that holds little grease and water compared with what your kitchen sends into it. A trap that suits a sandwich bar is small for a busy pub.

Most small traps are under-bench units that sit near the sink or dish area. They hold less than the in-ground tanks that larger kitchens use. Our guide to under bench vs in-ground grease traps explains both types. This article stays with the small end.

Small is a relationship, not a number

The size on the label tells you only half the story. The other half is how much fat, oil and food solids reach the trap, and how often. Two kitchens can own the same box and face very different problems.

Picture a trap sized for a cafe that serves toasties and coffee. It becomes small the day the owner adds a fryer, a rotisserie or a dishwasher with a high water output. Your fit-out and your menu decide whether the trap is still the right size.

What you gain and what you give up

A small trap costs less to buy and takes up less floor and bench space. In a low-grease kitchen, it does the job.

The trade-off is time. A small trap holds less grease before it stops separating properly, so it reaches its limit sooner. Once the grease layer and the settled solids fill too much of the tank, grease passes through to the sewer. Trade waste rules exist to stop exactly that. Sydney Water regulates what commercial kitchens in its area can send down the drain.

In plain terms, a small trap means:

• Cleans come around more often.
• Smells and slow drains show up sooner when a clean runs late.
• A busy week can push the trap past its limit before the next booking.

You pay less for the trap itself. You pay for its upkeep across more visits.

The worked example: keep it, service it more often or replace it

Here is the decision a small-trap owner actually faces. This example leaves out dollar figures on purpose, because your quotes and your agreement supply them.

Take a takeaway shop with a small under-bench trap. The owner adds a second fryer in March. By May the trap smells every second week, and the floor waste drains slowly after lunch.

The owner has three options.

1. Keep the trap and clean it more often. This works if the extra visits cost less over a year than a new trap, and if your trade waste agreement allows the shorter interval. 2. Keep the trap and cut what goes in. Scrape plates dry, wipe pans before washing, and stop tipping fryer oil or oily sink water down the drain. This reduces the load but does not remove it. 3. Replace it with a larger trap. This makes sense when the extra cleans add up to more than the install cost, or when the kitchen has changed for good.

The rule is simple. Add up a year of cleans at the shorter interval. Then ask your cleaner or plumber what a larger trap costs. If the two figures are close, choose the larger trap, because it also gives you a buffer for busy weeks. If the cleans cost much less, keep the small trap and book it on a fixed schedule.

Take the cleaning figure from real quotes. You can get three grease trap quotes and see how cleaners price the same small trap.

Can you just add a second small trap

Owners ask this often, and few guides answer it. Two small traps do not always equal one larger trap. Authorities usually set rules on the size and type of device that serves a kitchen. A second unit also changes your plumbing, your access and your cleaning bill.

Before you buy anything, ask your water authority or a licensed plumber whether a second unit meets your approval. Do not assume it does. Get approval first, then buy.

Check your trade waste agreement first

Most operators only think about the trap when it smells, backs up or faces an inspection. That is a poor time to learn the rules.

Your trade waste agreement with the water authority sets the pump-out frequency for your kitchen. Many owners do not know what theirs says. A small trap often carries a shorter required interval than a large one, so read your agreement before you plan your cleans. Our post on the five lines every kitchen owner should check walks through what to look for.

If you cannot find your agreement, ask your water authority for a copy. The NSW EPA and the Water Services Association of Australia publish general information on trade waste and water industry practice. Your local authority still sets the rules that apply to you.

Keeping a small trap working between cleans

You cannot stretch a small trap far, but you can protect it.

Daily habits

• Scrape plates and pans into the bin before washing.
• Wipe grease from pans with paper first.
• Keep fryer oil out of the sink and send it to a used oil collector.
• Fit sink strainers to keep food solids out.

Weekly habits

• Check the trap lid and any smell around it.
• Check the floor waste for slow draining.
• Write down the date of each clean. A log shows an inspector you are on top of it.

Resist the urge to scoop out the trap yourself between visits. Our guide on whether you can clean a grease trap yourself explains what you can do and what needs a licensed cleaner. Waste from a trap has to go to a proper disposal site, and that is the cleaner's job.

When a small trap is the wrong size

Watch for these signs:

• The trap needs cleaning well before each booking.
• Smells return within days of a clean.
• Your kitchen has added equipment, longer hours or a new menu.
• Your cleaner tells you the trap fills faster than its schedule allows.

If two or more apply, price a larger trap. Standards Australia publishes the plumbing and drainage standards that installers work to, and a licensed plumber can tell you which ones apply to your site.

A cleaner who sees your trap often gives good advice. Cleaners price on trap size, service frequency, access and disposal fees, so two kitchens with the same trap can get quite different quotes. Compare offers before you decide, and read more on the Grease Trap Quotes blog.

Get a quote for your small trap

If you run a small trap, the cheapest thing you can do is stay ahead of it. Grease Trap Quotes sends you three quotes from licensed cleaners by SMS, usually within about a minute of your request. Get three grease trap quotes and see what a regular clean of your trap really costs.

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Related reading: Grease Trap for a Kitchen: Which Drains Must Connect to It?.

Related reading: Grease Trap Servicing Words Decoded: What Pump-Out, Desludge and Full Clean Mean on Your Quote.