Just found this site today and I'm amazed by all the info. Hope somebody can answer a question for me. I am remodeling an older house. I am redoing an upstairs bathroom and kitchen. The kitchen sink has its own vent going to the roof. It is 15 feet from the cast iron drain / vent pipe that it is connected to. The cast iron drain / vent pipe is what the sink bathtub and toilet drain into and vent from. I am moving the location of the sink, tub and toilet upstairs and so I wish to remove the cast iron drain / vent pipe. Any advice would be greatly apprectiated, especially on how to remove the cast iron pipe, how to connect (to code) the new pvc pipe to it, the order in which the 3 separate drains have to be connected in and how to tie this all in to the vent to the roof and if I even need the kitchen sink to have its own vent if it is connected to the main vent. Sorry for the rambling. Pretty much the only thing that I know is that I should not have the pvc pipe sticking through the roof without shielding it from the sun :-)

Can you give a drawing of existing and proposed?

" Pretty much the only thing that i know is that i should not have the pvc pipe sticking through the roof without shielding it from the sun :-)"

I live in SouthWest Florida and ALL of our PVC vents are out in the sun. With schedule#40 PVC you'll have no worries about "shielding" the vent from the sun, ( or was that a joke? )

"how to remove the cast iron pipe, how to connect (to code) the new pvc pipe to it,"

How to dismatle cast iron? You start from the top and work down fitting by fitting. The easiet way is to whack it with a heavy hammer unless you're trying to salvage the cast iron. Wear safety googles when you do this to protect against flying chips.
You can convert to PVC in a number of ways but the one I use most is let a piece of bald cast iron stick out from a fitting and using a N0-Hub Band connect the PVC to it.

"Any advice would be greatly apprectiated, especially on the order in which the 3 seperate drains have to be connected in and how to tie this all in to the vent to the roof "

Let me show you how a typical bathroom's roughed in. Most bathroom groups are roughed in like this.
Toilet connects to sewer main or stack vent. Lavatory connects to toilet drain and runs a vent off the top the stubout tee out the roof or revents back into a dry vent in the attic.. The toilet wet vents through the lavatory vent and the shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes and also The Standard Plumbing Code Book Only one vent's needed and that can run up in the attic and revent back into a existing roof vent.

DO I even need the kitchen sink to have its own vent if it is connected to the main vent.

That "main vent" isn't a vent any more if you have a upstairs bathroom draining into it. It's a stack vent and you can't vent your kitchen sink into it.
However, you can run a separate vent off the sink up and tie it into the existing vent stack at least 6 inches over the flood rim of the lavatory.

Good luck, Tom

Thanks for the advice :-) Hoping to get started as soon as it warms up outside...