We used to get the occasional clogged lav dump chute. We would run the engines and pressurize the plane with the cabin superchargers or turbocompressors, then have the lav man open the valve, and the pressure would force everything into his hose and into the truck tank. Some lav men were afraid that the blast would be a little upsetting, so they sometimes failed to show up for one of those calls.
A couple of my co-workers had a clogged dump chute on the toilet tank. Jet engines are started by lots of compressed air through a 5 or 6 inch hose, connected to the airplane. The air spins a turbine starter. In those days, a start cart provided the air to start engines.
The engines could not be run for some reason, so one guy had the idea of holding the start hose up to the tank drain outlet to blow the blockage back up into the toilet tank to clear the blockage. He told his partner to go up in the lav and stand on the toilet lid to keep everything inside the toilet. Well, the upstairs guy had second thoughts, and just closed the door and stood outside the lav. Well, when it was all over, there were stalactites and TP hanging from the lav ceiling, and the mirror lights were arcing and smoking. The cleaners refused to go near the lav, so the guys had to clean it up themselves.
They ended up using a steam cleaner after putty knives, mops and a garden hose didn't do the job. The steam loosened the vinyl wall covering, so they had to glue it back on. They couldn't get that blue-green stuff, so they used Pliobond, which leaves a horrible odor, particularly in a closed lavatory. It also softens some vinyl and makes it blistery. The lav ended up being blocked closed, but the flight came back after takeoff because of odor complaints at the rear of the airplane. It ended up out of service until the smell left. The guys never lived it down to this day, and that was mid-sixties.
The guy who thought it up has transferred to a couple of different stations, and the story follows him. He ended up as a tech crew chief, telling other guys how to clear lavs. I think he is retired now, but the story lives on.