The Surprising Reason Your Grease Trap is Always Backed Up

We see it over and over again. Certain clients have recurring problems with backed up grease traps. The system gets clogged, a professional comes and removes the blockage, all seems fine, but it’s not long until the trap gets backed up all over again. Why?

The grease trap itself was installed backward. That’s right; the plumber who installed the trap made a mistake and now the restaurant is paying the price. Believe it or not, this happens in about 25% of restaurants.

Unfortunately, once a trap is installed backward, there isn’t much you can do other than regularly clear the grease trap clog, reinstall the device, or switch to a new indoor machine.

You need a certified plumber to install your trap, but just because the individual is a plumber doesn’t mean they are experts in grease trap installation. Here’s what you should look for during the installation to prevent headaches and grease trap clogs later on.

How a Grease Trap Works

The problem is most common in restaurants that use hydrostatic traps. These grease traps use good old gravity to separate the fats, oils, and grease (FOGs) from waste water, rather than moving parts like wheels and skimmers to push the oil off of the surface. In the picture below, you’ll see that hydrostatic grease traps are not symmetrical.

The “in port” is on the left, and the “out port” is on the right in this example. The in port will usually be positioned near the top, while the out port is near the bottom.

Above is a side view of the a grease trap. Water, solids and grease enter the trap and slowly separate. Oils rise to the top while solids fall to the bottom and relatively clean water flows through the middle. The two baffles act as walls to prevent the oils and solids from following the water to the out port. As it reaches the out port, a “flow restrictor” ensures the oils have had ample time to separate from the wastewater.

When an inspector visits your restaurant, they’ll take a sample from the flow restrictor. When the machine is installed incorrectly, you may fail inspections or receive citations because samples taken from this area won’t have flowed through the machine yet.

Make sure your plumber installs the system so your FOGs are entering your trap through the in port and exiting through the out port. If not, you’re going to end up with a constantly clogged grease trap.