Why does my grease trap always appear full?

Understanding why your grease trap always appears full, but seems to be working, requires an understanding of how grease traps work.  Grease traps work on two principles: FOGs (fasts, oils and grease) are lighter than water and food waste is heavier than water. 

A grease trap works like this-

In a grease trap, a mixture of fats, oils, grease, water and food waste all enter the trap (usually a large box) through an inlet pipe. The job of a grease trap is to separate the FOGs, water and food waste into 3 layers. This mixture is separated into layers so that the waste water can pass through the trap and empty into a municipal wastewater or sewer system. The trap retains the fats, oils and grease in the top layer and the food waste in the bottom of the trap. The water from the trap needs to be clean enough to pass through the pipes of the sewer system without clogging and blocking the flow.

Why we think the grease trap is full

The FOG layer on the top builds up and thickens over time, as does the food waste layer on the bottom. Even as those layers form, water flows through the trap and raises the level of the FOG layer on top. Looking down from above onto the FOG layer it can appear that the trap is full. Many times the trap is NOT full.

What we are looking at from above is the FOG layer being raised by water flowing through the trap. The trap may be functioning perfectly even though we see a layer of oil and grease on top. Looking down at the FOG layer is not a reliable way to determine if the trap is full or not functioning. You should see the FOG layer and if you see it, it does not mean the trap is full. The trap may just be doing its job.

How you know if your grease trap is full

It is commonly accepted that a grease trap may begin to fail(clog and backup) when the combined height of the FOG and food waste layers are more than 25% (the 25% rule) of the total height of the contents in the trap. This is something that is not simple to observe.

Some grease traps have a window with an observable 25% mark which makes it easy to know if a trap should be pumped and cleaned.

Other traps may require the use of a sludge judge. A sludge judge or a Dip-Stick Pro measures grease and solids in a tank by taking a sample with a transparent cylinder. You measure the FOG layer and then the food waste layer and calculate the combined total as a percentage of the height of fluids in the grease trap. Anything approaching 25% should be pumped immediately.

{(Height of FOG layer + Height of Food Waste)/Total fluid height}<25%

Signs your grease trap is full

A full grease trap can cause blockages and foul odors. Here are 7 signs that your grease trap might be full:

• Slow drains: Water in the sink stands or drains slowly, even if there’s no visible clog.
• Bad smells: A lingering smell of grease or oil, especially near sinks and drains. The odor might even back up into the kitchen.
• Grease leaks: Grease spills out of sinks, pipes, or water lines.
• Overflowing: Grease overflows from the trap.
• Increased pests: You notice more fruit flies.
• Unusual noises: You hear strange noises coming from the trap.
• Grease accumulation near inlet or outlet pipes.

If you are experiencing one or more of the signs listed above call D&W Alternative Energy and ask them to check your grease trap and pump it if they determine it is necessary. 

If your grease trap truly is full quickly after pumping then your grease trap may be undersized or you have outgrown it.