Grease down the drain?

I had this pan with about a half-inch of grease in it from heating gyros. It’s a pain to pour it off and put it in a container to throw out.
Of course I learned early that you shouldn’t pour grease down the drain because when it cools it can congeal and cause a drain blockage.
But what if you take some detergent and mix it with the grease? Just a squirt, but enough to combine and keep the grease from congealing.

Is there any other reason that putting grease down the drain in this manner is a bad idea?