Clean cake (6)
I believe the answer is:
sponge
I believe this is a double definition.
'clean' is the first definition.
(I've seen this before)
'cake' is the second definition.
(sponge cake is a kind of cake)
(Other definitions for sponge that I've seen before include "Sea creature often found in bathroom" , "Porous mass in oceans" , "Bum - cleaner" , "Porous substance to soak up" , "Heavy drinker" .)