Mesh bag carrying flask right at the bottom (10)
I believe the answer is:
nethermost
'the bottom' is the definition.
(I've seen this before)
'mesh bag carrying flask' is the wordplay.
'mesh bag' becomes 'net' (I can't justify this - if you can you should give a lot more credence to this answer).
'carrying' means one lot of letters goes inside another.
'flask' becomes 'thermos' (thermos is a kind of flask).
'net' enclosing 'thermos' is 'NETHERMOST'.
'right at' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for nethermost that I've seen before include "located in lowest position" , "at the bottom of the pile" .)