Bill after turning from gas is steep (5)
I believe the answer is:
bathe
'is steep' is the definition.
(steep can mean to soak or bathe in a liquid)
'bill after turning from gas' is the wordplay.
'bill' becomes 'tab' (a tab is a bill at a bar).
'after turning from' shows that the letters should be reversed in order (some letters turn away from others).
'gas' becomes 'he' (chemical symbol for Helium).
'tab' in reverse letter order is 'bat'.
'bat'+'he'='BATHE'
(Other definitions for bathe that I've seen before include "Wash, soak" , "Wash in water" , "Go swimming" , "Swim for pleasure, and clean oneself" , "Cleanse the body" .)