Actually, that Air France 737-200 looks like it dumped lav-juice out onto the fuselage.
It's a common occurence if the aircraft isn't serviced properly, which is frequently the case with contract service. I think the Lav guy was lazy and didn't seal either the dump valve or the fill valve properly. Either way, it would drain out slowly, leaving streaks just like that.
Vanguard had this happen frequently. It just didn't show up on aircraft very well because of the old 737 paint scheme. The only time you ever saw it was when the MD
-80's front lav was serviced improperly, and boy did I hate cleaning that sh*t up (no pun intended).
Those who fail to learn history are doomed to repeat it in summer school.