replacing cast iron pipe

I have what I think is going to be a pretty significant job so I want to get as much of it planned out and prepped ahead of time as I can. To that end I am looking for answers to some specific questions as well as any advice or suggestions.

My wife and I have been in this house for just over a year and the excitement I have found as I have been doing repairs is truly something. My wife often hears me use the term halfass to describe what I find in the walls and basement.

The adventure is surrounding the kitchen sink which is in an addition to the house which is over an addition to the basement. The problems are as follows:

• The kitchen sink drains very slowly
• There are a couple of leaks in the cast iron pipes
• There is a standard S trap under the sink but a second old school drum trap in the basement
• In the basement, before the drum trap, the dishwasher drain connects
• The first 6 feet of drain are nearly dead level
• The vent pipe connects along side of the drain pipe then runs about 8 feet horizontal before turning up to vent.

The first picture from the left is the vent pipe, then there is the drum trap. The vertical pipe is the sink drain and the horizontal pipe is the dishwasher drain. The wall at the back separates the basement addition from the rest of the basement.

The second picture is the collection from a different angle.

After going through the separating wall the pipe drops straight down then continues along the wall. (picture #3)


Up to this point all of the drain piping has been PVC or copper while the vent line has been cast iron. You can see where the copper connects to the original cast iron. This cast iron continues all the way to the main sewage connection where it joins up with the drain from the bathroom sink. From the kitchen to the sewage connection is about 40 feet.


Picture #4 shows three connections to the main sewage line. The left most pipe connects the two toilets and showers. The middle pipe connects the first floor bathroom sink. The right most connection is from the kitchen. The black tape was put there by the previous owners to cover up one of the two leaks.

The other leak is where the first floor sink drain comes through the basement ceiling. (picture #5) The white stuff is some sealant that I put there as a temporary hold.

So my plan is to cut the Y pipe (picture #6), put on a flexible coupling, and a new Y pipe.

Remove all of the piping from the first floor bathroom sink and all of the piping from the kitchen. Reroute the dishwasher drain back up into the kitchen and connect above the S trap.

So here are my questions in no particular order.
• I know ¼” per foot is the minimum but what is the maximum pitch?
• If I keep the vent pipe at the minimum pitch how long can it run horizontally??
• Is there any disadvantage with the vertical drop after coming through the wall as seen in pic #3?
• How close to the basement wall can I wall can I run the pipe??
• To drain a kitchen sink and a dishwasher what diameter pipe should I use??
• How much cast iron pipe do I need to leave at the Y pipe to connect the flexible coupling??

Any other thoughts or suggestions??