This is a homophone clue - look for indicators like 'we hear', 'sounds like', 'say', 'aloud', or 'reportedly' - the answer sounds like another word
Break down the clue into definition and wordplay parts
Answer: PAINTSTRIPPER | Definition: 'thinner, say?' | Wordplay: Toulouse-Lautrec was an artist known for portraits of prostitutes i.e. ‘PAINT [a] STRIPPER’ might be something he would do