Toilets revolting; and that's an understatement (7)
I believe the answer is:
litotes
'that's an understatement' is the definition.
(thesaurus)
'toilets revolting' is the wordplay.
'revolting' indicates an anagram.
'toilets' is an anagram of 'LITOTES'.
'and' is the link.
(Other definitions for litotes that I've seen before include "Town of N. Norway" , "No exaggeration" , "Possibly, no small surprise" , "in which not a little is a lot?" , "Understatement for rhetorical effect" .)