Mixing paint, slipshod in cleaning of equipment (4,3,6)
I believe the answer is:
spit and polish
'cleaning of equipment' is the definition.
(spit and polish can mean cleaning something)
'mixing paint slipshod' is the wordplay.
'mixing' indicates an anagram.
'paint'+'slipshod'='paintslipshod'
'paintslipshod' is an anagram of 'SPIT AND POLISH'.
'in' is the link.
(Other definitions for spit and polish that I've seen before include "Punctilious attention to cleanliness, discipline, etc" , "Careful procedures" , "Thorough cleaning of kit" , "Thorough polishing" , "Military attention to neatness" .)