The incident I referred to was a 777. I took a pic of the resulting mess on the ramp, but it doesn't do it justice. 744s are also fun, in that there are about 9 different drains that lead to the forward mast.
3000psi from an n2 rig attached to the mast normally clears it!
Reminds me of something I saw in the 80s. CO had just gotten 4 A300s from Eastern, and I watched as some of their techs tried to deal with a blocked rear lav. Apparently they thought it would be a good idea to hook up an airstarter to the dump chute and give it a blast. They had a guy in the lav holding a blanket over the toilet (must have been junior). Long story short, I don't know what happened to him, but these aircraft had lav walls made of vinyl with holes about every 1/4 inch (for acoustic suppression?) and most of the holes were filled!