How can you stretch your anal opening to a huge size?

It depends on your age. How old are You. You. really don't want to stretch yourself too much because it will make it harder to hold in your poop. To stretch yourself or prepare for anal sex there are butt plugs that work very well. They have different sizes and if you have never used one before I suggest starting with the beginner and moving up in size only when you feel comfortable to go to a bigger size.