I have a 40cm toy (this
) that I bought specifically for going deep.
Do you know about the sigmoid colon? (If you do, you can ignore most of this post).
A little less than 20 cm deep you should encounter it, and it's basically another valve that you need to open before you can continue. Basically, make like you're trying to poop and it will open and you can easily push through.
Pushing against a closed valve can sometimes hurt but with practice it becomes a bump more than an obstacle. A long flexible toy, like I presume you have, is good for practicing.
In my experience, once you go passed that point you can just keep on pushing it in. The only limitation is the natural curvature of your bowel and the flexibility of your toy... and obviously your bowel needs to be empty, which might require a long douche session.
It feels really weird so I haven't taken all of it, but I've taken 70-80% at least. It's fun to see how deep you can go. Just remember the usual rules of anal play. Good hygiene. Go slow. Lots of lube.