Clueless, you should clean your grease trap at least every other month. Doing it frequently will keep the job short and easy.
Here’s how it works:
The grease floats to the top and builds up on the sides of the trap. The water flows straight out the side on the bottom. If it has been 3 years, I’ll guarantee you that the trap is filled to the top with grease, and the grease is flowing straight out into the sewer system because it has no where else to go.
You might think “who cares,” but you’re responsible for your sewer pipes until they tap into the public system. Not cheap to tear up your parking lot/yard to have your blocked pipes cleaned. Our sewer pipes have about 50-60 feet until they tap into public. Chances are, most of that grease would settle long before it reaches the public system. We are inspected occasionally by our township, and subject to fines and headaches.
Wear long gloves, scoop the crap off the top with a paper cup and put it in a bucket. Take a scraper (like a spatula) and scrape down the sides, then scoop that off the top. Run some water, scoop the leftovers.
This job is usually saved for people who are on their way to being fired. However, I rarely fire people. So, they get to clean the grease trap and that has sent more than a few people over the edge.