Use soft soap - it's not so lumpy (7)
I believe the answer is:
flatter
I believe this clue is a double definition.
'use soft soap' is the first definition.
(to use soft soap informally means flattery)
'it's not so lumpy' is the second definition.
(flatter and therefore not as lumpy)
(Other definitions for flatter that I've seen before include "when all smoothed out?" , "drier" , "Lavish compliments on (someone)" , "suit, looking good" , "resort to cajolery" .)