Clue: Disinfectant from Spooner's cavernous vessel (5,3)
Answer: SHEEP DIP
Explanation: Definition: Disinfectant
=an insecticidal disinfectant used on sheep
 Spoonerism of 'D-eep Sh-ip', or "cavernous vessel"
 Slightly unfortunate re-use of 'ship'='vessel' from 17ac