: I am putting a bathroom in my basement next to an existing stack - I am connecting the toilet to the main sewer line - can I vent the toilet into the this stack or do I have to vent it elsewhere - does it make a difference if there is a window down there for circulation. Also, should I use PVC or Cast Iron to connect to the main sewer line and what size??

I would vent the toilet either to a vent stack or add another vent. You could also use a air emitter like a Studor vent also.

Windows don't count for venting. Even if Bill Gates were to sell it to you.

To connect to the existing cast iron pipe, I like to use a cast iron fitting, then from there it can be plumbed using plastic fittings. Terry