I use an appropriately sized box end wrench and slip over the tube and bottom against the crimp in the tube and tap it in with a small hammer. Some grease on the end that presses into the block will help it go in a little easier.
I take it you got the old broken piece out?
I usually just polish the end with emery cloth and use a little grease.
It really was never a problem getting a new tube in, but getting the old broken piece out can be a bear. I've found an easy-out is the best for getting the piece out.