How toper opens more rum, swigging large tot (7)
I believe the answer is:
toddler
'large tot' is the definition.
'toddler' can be an answer for 'tot' (I've seen this in another clue). I'm not sure about the 'large' bit.
'how toper opens more rum swigging' is the wordplay.
'how' becomes 'l' (I can't explain this - if you can you should believe this answer much more).
'opens' suggests taking the first letters.
'more rum' becomes 'odder' (rum can mean odd).
'swigging' is an insertion indicator.
The initial letter of 'toper' is 't'.
't'+'odder'='todder'
'l' put into 'todder' is 'TODDLER'.
Can you help me to learn more?
(Other definitions for toddler that I've seen before include "Feeble walker" , "Young child" , "One is learning to walk" , "Small child" , "Child starting to walk" .)