Bathroom walls dry in house (5)
I believe the answer is:
lotto
'house' is the definition.
(I've seen this before)
'bathroom walls dry' is the wordplay.
'bathroom' becomes 'loo' (loo is a kind of bathroom).
'walls' means one lot of letters goes inside another (to 'wall' can mean to contain).
'dry' becomes 'tt' (short for teetotal - no alcohol).
'loo' placed around 'tt' is 'LOTTO'.
'in' acts as a link.
(Other definitions for lotto that I've seen before include "Prize draw" , "Game of chance similar to bingo" , "form of gambling" , "Game of chance based on numbered balls being drawn at random" , "National gambling game" .)