1 especially British EnglishTBC
a pipe that carries water or waste liquids away:
The flood was caused by a blocked drain.
There's a problem with the drains.
2TBC British English
the frame of metal bars over a drain where water etc can flow into it [= grate American English]
3 American English
the hole in the bottom of a bath or sink that water flows out through [= plughole British English]
something that continuously uses a lot of time, money etc:
The war was an enormous drain on the country's resources.
if time, effort, or money goes down the drain, it is wasted or produces no results:
Well that's it. 18 months' work down the drain.
if an organization, country etc goes down the drain, it becomes worse or fails:
That's why this country's going down the drain!