The Blame Game
To 'put' something somewhere requires an intention. There is no need to make such a claim in order to explain the presence of coffee grounds in sinks and drains.
On a SIN/LHR sector in each J/C galley the crew would make and clean at least 10 bodums (coffee-plungers) of coffee and a similar number of bodums of tea. If from each of these 12 cup bodums just 5 coffee grounds or 5 tea leaves found their way into the sink, then by the end of that one sector there would be 50 coffee grounds and 50 tea leaves from each galley. Add to that the possibility that when opening the vacuum sealed packs of coffee they can suddenly give way and shower coffee around or a hole might be torn in the side of the packet which makes spillages likely.
The point is that no matter how careful the cabin crew are when cleaning these bodums SOME coffee grounds and tea leaves will inevitably end up in the sink. Even a small number when multiplied will result in an accumulation.
Before claiming cabin crew are being irresponsible and blaming them for blocked drains why don't you put yourself in their position and make up a bodum of coffee, let it brew for a while then plunge it. Come back in a few minutes and empty it and clean it. Make sure there are no grounds left on the top of the plunger as these will end up in the cups of the next drinkers, be they passengers or crew and they will complain bitterly. Try doing it in the upper deck galley on the 747 or in the front galley on the 767. Try doing it with bottles of wine, juice, water etc on the bench.
I have never ever seen cabin crew put coffee grounds or tea leaves in the sink. I have never ever seen cabin crew pour milk or yoghurt or orange juice down the sink. I have seen 'helpful' passengers pour milk or juice down the sink if they take a glass back to the galley on their way to the toilet. Working in such a confined space, it is, however, inevitable that the occasional spillage will occur.
Boeing place drip trays on the aircraft because it is highly likely that spillages or blocked drains will occur. When those drip trays are cracked the swiss cheese is all lined up.
Obira