I have just added a new shower to an existing bathroom with just a toilet. I would like to tap the shower drainage line into the toilet line that is running out of the house into our septic tank. I have never tapped into an active line. Advice on what tools, and techniques should be used to tap into the line would be helpful.

Thanks

A few questions first to help me understand where you are in this project. Did you properly trap the shower and also provide venting or not? What material is you drain pipe and is it exposed or in concrete

I have just added a new shower to an existing bathroom with just a toilet. I would like to tap the shower drainage line into the toilet line that is running out of the house into our septic tank. I have never tapped into an active line. Advice on what tools, and techniques should be used to tap into the line would be helpful.

Thanks
You do realize that the shower will have to be vented don't you? You haven't given us much to work on. We don't know what material the pipes are and how much plumbing experience you have. Bare bones explanation?
Cut the toilet line and install a wye or a combination wye and eighth bend to pick up the shower. Ahead , and downstream, of the shower trap roll a 2" wye up 45 degrees and take off a vent that will run out the roof or revent back in the attic to a existing roof vent. This will bring you up to the trap and trap raiser that will be positioned directly under the shower drain. Do you have the necessary plumbing skills and tools to do this? Regards, Tom