Concocted a lethal brew, dropping bottom bits, to make infusion (6,3)
I believe the answer is:
herbal tea
'concocted a lethal brew dropping bottom bits' is the definition.
I can't tell whether this defines the answer.
'make infusion' is the wordplay.
'make' becomes 'herbal' (I can't justify this - if you can you should give a lot more credence to this answer).
'infusion' becomes 'tea' (I've seen this before).
'herbal'+'tea'='HERBAL TEA'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for herbal tea that I've seen before include "healthy drink" , "liquid concoction" , "hot drink" , "Plant infusion" .)