I'm doing some renovations in a home built in the mid 50's. The waste lines are all cast iron. The toilet flange needs to be replace so I have decided to change all waste lines to PVC.
The toilet has a 4" bend with a 2" connection for the tub drain. The line drops below the floor about 6" to 8", bends and runs perhaps 14" into the vertical waste, which is 3". The vert. waste line above the toilet connection is reduced to 2" and it runs up through the floor into the bathroom for vanity drain and out the roof for venting.
Question: Is it necesary to use 4" for the toilet or can I get by using 3" for such a short run? Does the tub drain have to tie into the toilet line or can it be connected to the vert. waste with a wye? Are there any restrictions as far as how close these drains can be placed on the vert. waste? Will I need to make any changes as far as venting is concerned?
Thanks so much for your time,
John

Good morning John,

"Question: Is it necesary to use 4" for the toilet or can I get by using 3" for such a short run? Does the tub drain have to tie into the toilet line or can it be connected to the vert. waste with a wye? Are there any restrictions as far as how close these drains can be placed on the vert. waste? Will I need to make any changes as far as venting is concerned?"

Yes, you may drop to 3" to pick up the toilet. The tub drain may be connected to the 3" vertical waste line providing it ties in ABOVE the toilet,(You can not discharge a major fixture past a unvented minor one).
Will this job be permitted and inspected. If not then if it's worked for the last 50 years I'd leave the venting alone. If you've pulled a permit then the distance between trap and vent is 1 1/2" drain 3 1/2" feet, 2" drain 5', 3" drain 6',and a 4" drain 10'. Good luck and if we can be of more assistance feel free to post back. Regards, Tom

Tom, thanks for the quick response and advice. As I suspected but wanted to hear it from an expert.
Thanks again, John