Careless about emptying the plant's discharge (5)
I believe the answer is:
latex
'plant's discharge' is the definition.
'latex' can be an answer for 'discharge' (latex is a kind of discharge). I'm unsure of the 'plant's' bit.
'careless about emptying the' is the wordplay.
'careless' becomes 'lax' (synonyms).
'about' means one lot of letters goes inside another.
'emptying' says to hollow out the word (remove centre letters).
'the' with its middle removed is 'te'.
'lax' enclosing 'te' is 'LATEX'.
Can you help me to learn more?
(Other definitions for latex that I've seen before include "Milky substance from rubber tree" , "Tree fluid used to make rubber" , "Milky fluid produced by plants" , "Milky sap of rubber tree" , "Stretchy stuff" .)