Do Ice Cubes in the Black Tank Really Work?

Yes and No, I think this practice started on modern aircraft with the vacuum toilets. The "Black" tanks have 2 sensors that signal when the tank is full at that point they no longer flush to avoid over filling, this usually means the aircraft is grounded. and it's a big job to get access to the sensors. Someone discovered that by dumping a bag of ice cubes into the very most forward toilet on that tank then tricking the lav system to flush once the ice cubes travel down the pipe at very high speed entering the empty tank and shattering into many pieces knocking the waste from the sensors. Works almost every time on the "500 mph S**t sucker" toilet system, not so much with the static toilets on older aircraft or an RV.