Shower in toilet is hot (6)
I believe the answer is:
lavish
'shower' is the definition.
(synonyms)
'toilet is hot' is the wordplay.
'toilet' becomes 'lav' (lavatory).
'hot' becomes 'h' (abbreviation eg on taps).
'lav'+'is'+'h'='LAVISH'
'in' is the link.
(Other definitions for lavish that I've seen before include "Sumptuous" , "Spend(ing) generously" , "Rich, elaborate" , "Sumptuously rich" , "Heap (money)" .)