How can I tell my girlfriend about my belly button fetish?

I don't have a gf yet but when I get one I want to be able to tell her about my belly button fetish. I want to be able to stick my finger in her belly button and wiggle it around to make her laugh. When she's stretching I want to be able to stick my finger in it and when she's reaching to get something I want to be able to come up behind her and grab her belly, tickle it and tickle her belly button from behind. When we are laying down I want to be able to reach over to tickle her belly button and then blow raspberries on it. I want the girl to be accepting of my fetish and I want her to let me do this stuff to her. How can I tell her about my belly button fetish?