Toilets: you must replace old taps (4)
I believe the answer is:
bugs
'taps' is the definition.
(I know this)
I cannot understand how the remainder of the clue works.
(Other definitions for bugs that I've seen before include "Secret listening devices" , "Creepy-crawlies in computers" , "Small crawling creatures or disease-germs" , "Insects or faults in a system or machine" , "Software problems" .)