Everybody in drag, it seems, is fat (6)
I believe the answer is:
tallow
'is fat' is the definition.
(fat used to make candles)
'everybody in drag' is the wordplay.
'everybody' becomes 'all' (all people).
'in' indicates putting letters inside.
'drag' becomes 'tow' (towing is a kind of dragging).
'all' going into 'tow' is 'TALLOW'.
'it seems' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for tallow that I've seen before include "Animal fat used to make ..." , "Candle wax" , "Fat processed for making candles" , "Animal fat used in candles, soap etc" , "Fat used in candles/soaps" .)