Loosen black tile occasionally that's on the house (7)
I believe the answer is:
freebie
'that's on the house' is the definition.
(a freebie is given away for free or on the house)
'loosen black tile occasionally' is the wordplay.
'loosen' becomes 'free'.
'black' becomes 'b' (as in pencil classifications).
'occasionally' means one should take alternating letters.
The alternate letters of 'tile' are 'ie'.
'free'+'b'+'ie'='FREEBIE'
(Other definitions for freebie that I've seen before include "Present" , "Something given without charge (colloq.)" , "treat" , "Uncharged-for item" , "Something had without paying" .)