Three inch is the hardest of the lot because it is the smallest.
Get the pipe on a flat surface seam side up with the receiver side away from
your body. Your hands should be in the middle of the 6' length, 18-24"
apart. Insert the lip of the pipe into the flange, making sure that the
entire length is inserted then you have to press down gently and it will pop
in. When you are pressing down gently you are converting a circle to the top
of an apple shape (when viewed from the side perspective).
If the ends are not aligned just stand the pipe on one end and use a hammer
and block of wood to align the ends.
I hope you can follow that. It is easy after the first time. But darned
hard to write an adequate description.