Mine didn't fit very well, but I did manage to get it in eventually. I had to unscrew the deck almost all the way out, got the plug started, then kept pushing it down as I tightened the deck.
I guess it also depends on which deck you have. It will only work on the decks with 4 wicking holes. (Some only have 2)
I remove the screw on piece, place the rubber piece on, then put the screw ring on and screw it down. Then I wick it.