Grease traps are nasty!
I knew a few people that had septic tanks, and grease traps on the kitchen drain lines. One of them was my mom's friend Marguerite, and I remember them having trouble with it the day we visited them in late Winter '62. She had fixed a nice lunch for us, and when she was cleaning up after we ate, the sink drain was clogged. When she turned on the disposer, the dirty water came up in the other side of the sink. She had their son get a plunger. She plunged on the disposer side while my mom held the stopper down on the other side. The water went out of the sink, but when Marguerite opened the Frigidaire dishwasher, a tidal wave of yucky water ran out across the floor. We had to get towels to wipe it up. Her husband Bill then went to the basement and proceeded to clean out the grease trap.
I also worked at a Steak 'N Shake restaurant during the Summer of '78, and they had a problem with the grease trap clogging one evening. Water from the dishwasher and sinks came up out of the floor drains, causing the restaurant to close so we could clean up. Luckily, the plumber was able to come early the next day to fix it.