Well this falls under the disgusting category. Now before I write this I want to say that I love Virgin Atlantic and fly them as often as possible and that I do believe this was a one time incident.
We were taxing out to the runway at LHR
for a flight to EWR
(747-400) and were seated in the second to last row at the back of the plane. As we were approaching the end of the taxiway (about number 3 for takeoff) one of the flight attendants behind us yells "Oh my God!", I turned my head to see the flight attendant on the other side turn her head and also yelled "Oh my God". One picked up the phone and to tell the pursur (I am not sure if that is the term they use for head flight attendant) that the toilets were overflowing. Sure enough, there was water pouring out from underneath the doors of all four toilets right behind us. A few flight attendants came running back form the front and started to close off valves in each bathroom. The pilot then came on the PA and told us that we were heading for a holding area so that they could determine what the problem was. Turns out that there was a blockage in one of the pipes somewhere that was causing all the system to run in reverse. A couple folks came onto the plane with some wet/dry vacs and mopped up the carpet once the blockage was cleared, but we still ended up flying all the way to EWR
with a distinctive odor trailing behind us.
Like I said, I love Virgin and am happy that I have had many memorable flights with them for reasons more positive than what is listed above.