On the subject of the contents of drip trays being reused, I remember some kind of TV thing on this - I don't know if it was a news report, or part of a documentary - about 35-40 years ago when for some reason the subject was topical, possibly there was a proposal to ban it? They were reporting from a pub, and as well as the drip tray being emptied into a glass to start the service of the next pint that was ordered, they followed the landlord round the pub at the end of the evening walking round the pub emptying the remains of unfinished pints into a bucket (presumably several buckets for different drinks, or at least one for lager and one for bitter but I don't remember that level of detail), then taking the bucket down to the cellar and pouring the contents of the bucket back into the beer barrel to sell again! I hope that's anachronistic now!