Dirty election must be oddly disregarded (7)
I believe the answer is:
pollute
'dirty' is the definition.
(polluting is a kind of dirtying)
'election must be oddly disregarded' is the wordplay.
'election' becomes 'poll' (I've seen this before).
'oddly disregarded' means one should take alternating letters (letters in odd-numbered positions removed).
'must'+'be'='mustbe'
The alternate letters of 'mustbe' are 'ute'.
'poll'+'ute'='POLLUTE'
(Other definitions for pollute that I've seen before include "Add impurities" , "Taint, foul" , "Contaminate; defile" , "Adulterate, contaminate" , "Make dirty or impure" .)