747s ( at least prior to the -8 ) had open-to-atmosphere grey-water drains; lav and galley sink water flushed out immediately. The problem with that is that they sing like organ pipes at 500 kt.
As a result the 777 has valve-operated drains which only open when there's a certain pressure of fluid in the system. Edit: and according to a web search, the 787 has no external drains at all; all grey-water is captured in the lav tanks.
Surplus milk and beverages are disposed of via the toilets.
Last edited by El Bunto; 2nd January 2016 at 06:32.