I have read about this many times but witnessed it first hand this past weekend at Hardy Lake in Indiana.
I pulled up to the dump station just as a gentleman and his wife were staring down the dump valves of their TT. My guess is that they weren't planning on anyone watching what they were about to do!
The guy reaches down, pulls his black tank valve and spews blue liquid w/chucks all over the dump drain as he holds it open with his foot. He then reaches down and dumps his grey tank!
I was really miffed to say the least so I of course had to go tell him "hey, they make sewer hoses every day"! He proceeds to tell me that this is not an issue because they "don't use their toilet"! So I have to ask...."if you don't use your toilet...where is the blue water coming from?" He does't really answer other than to repeat that they don't use the toilet!
I have to fall back to the old adage....You Can't Fix Stupid!
Where your gloves....this guy may be dumping his tanks before you do!