Difficulty rejoining cast soil stack
I pulled off a toilet to replace it and the flange and about a 3" piece of the soil stack came with it. The flange appears to be in decent shape so I'm just trying to figure out how to rejoin the soil stack. I believe it is cast iron and it doesn't appear to be soldered anywhere or threaded, but there is a small groove that runs through the two pieces. An associate at home depot agree with my assessment of the flange and suggested an expoxy to rejoin the two. I've put it all around the rim but the two pieces never seem to line up quite right and sit flush and the more I fight with it the more epoxy falls off.
Is there a trick to this or a better method to rejoin these??