There was dirty brown water pouring out of the galley near me in row 79 on a QF A380 on the way to LAX late July last year, though the crew mostly kept it at bay with what must have been 50kg of paper towel; only a relatively small amount ended up down the aisle.
The FA seated in the jumpseat right across from me at the time told me it was not uncommon, though I'm guessing not many of the plumbing dramas they've had previously are quite as bad as this one!