Humourous solution
I was on a flight on Virgin, IIRC, when the senior cabin crew (CSD or is that a BA-ism?) came on the PA just after touchdown, still taxying, and announced they were taking volunteers to help clean out the lavs after the flight. All you had to do to volunteer, she said, was stand up before the aircraft had come to a complete stop and the captain had turned out the seatbelt sign. Got a hearty laugh throughout the aircraft and made her point. Not a single pax stood up before said seatbelt sign was turned off.
Great way to see the problem coming and prevent it before it even happened, all with a nice touch of humour. Well done to her!
Flew Egypt Air earlier this year. Boatloads of pax up as soon as the wheels were on the ground, including crew, not a word was said to anyone, which rather meant it was acceptable. Cultural difference, maybe?
Pitts2112