Wells, Sump Pumps and Septic Sewage Systems - septic tank

I have an old septic tank that is still doing fine but this past summer the clay outlet pipe got clogged and I had to get a repair man in to unclog it. He did it by digging down and breaking through the pipe and running a plumber's snake into it. That opened up the pipe but he told me I should replace the old pipe from the tank to the distribution box. My question is this: what sort of flange or pipe is on the outlet of the steel tank? When I remove the old pipe I must replace it with plastic but I should prepare myself for a way to connect it to the tank.

Could be hard to figure, there are a number of different hook-ups, you may have to dig down and look for yourself, sorry. :(