Antiseptic creams or soap? Test half of each (8)
I believe the answer is:
creosote
'antiseptic' is the definition.
(creosote can be used as an antiseptic)
I don't understand the remainder of the clue.
(Other definitions for creosote that I've seen before include "Dark oily liquid, preservative for wood" , "Wood treatment" , "Wood preserver made from coal tar" , "Fencing gear, perhaps" , "Oily excretion" .)