Espied them back at the hotel mixing gin, while taking the odd gulp, with fluid kept beside the sink (7,2,6)

'fluid kept beside the sink' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'espied them back at the hotel mixing gin while taking the odd gulp with' is the wordplay.
I cannot quite understand how this works, but
'at' could be 'in' (synonymous in some cases - eg at school, in school) and 'in' is found in the answer.
'hotel' could be 'h' (phonetic alphabet) and 'h' is located in the answer.
'while' could be 'as' (eg 'while I walked' means 'as I walked') and 'as' is found within the answer.
an anagram of 'gulp' is 'gupl' which is located in the answer.
'with' could be 'w' (short for with) and 'w' is found in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?