I recently came across a convention called "Trash" which is designed to compete against 1 nt . My first question is, is this a legitimate convention?
If it is can I use this to defend against 1 club.
If you are playing in EBU events, then any defence to 1NT is permitted at Level 4. At Level 2 there are restrictions - with one exception 2-level overcalls must show an "anchor" suit.
Any defence is permitted at Level 2 upwards to a 1 opening which does not guarantee 3 cards in the suit.
At club level the responsibility for systems policy lies with the club.