How about you get a buttplug set, an aneros, a few dildos and a vibrator? You have to make your ass get used to big things instead of trying to force something too big into it because that would be very painful depending on the size of the object. Also, get an enema set or a douche so you can clean yourself. And don't forget to use lots and lots of lube. Sadly, the asshole can't create it's own lubrication like a pussy can.