The kitchen trap, was packed "solid". With something that wasn't grease. It didn't smell like grease, and it was packed down the whole drain beyond the trap. It smells like burned plastic. In a rental unit that I worked in today.

Garbage disposal?
Could it be paraffin wax?

Some of it is saponified grease which is a form of wax. It is produced from the reaction of grease and caustic making a waxy type soap and with the addition of salt, it precipitates out, not very soluble.

I would suggest to mix a cup of backing soda with a cup of table salt put it at the sink drain now add two cups of white vinegar leave it for a few hours then put very hot water in the sink to flush out every thing see if it will help, Thanks.

John

Ask your tenant, what they put down the drain. Also, there are certain cultures that cook meals we are not used to - then dispose of remnants into garbage disposer.

Milo