A few solutions that I've got but don't understand.
13a - recall one hundred odd swallowing drop of special medicine (7). Answer = nostrum
19d - even row about card game (2,1,3) on a par.
17d - Flush? Reportedly posted a trivial amount of money (3,4). Red cap. Means 'a trivial amount of money' but what does it have to do with Flush?
Any explanations appreciated!