Small amount of drink mopped up by a tissue, falsely? That's an understatement (7)
I believe the answer is:
litotes
'that's an understatement' is the definition.
(I've seen this before)
'small amount of drink mopped up by' is the wordplay.
'small amount of' becomes 'lies' (I can't justify this - if you can you should give a lot more credence to this answer).
'drink' becomes 'tot' (a small alcoholic drink).
'mopped up by' indicates putting letters inside (inserted letters get eaten or 'mopped up').
'lies' placed around 'tot' is 'LITOTES'.
'a tissue falsely?' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for litotes that I've seen before include "No small task, for example" , "Rhetorical understatement - toilets (anag)" , "Understatement for rhetorical effect" , "Figure of speech about toilets" , "No exaggeration" .)