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Old 04-25-2011, 10:25 PM   #1
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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 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??
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Old 05-20-2011, 10:16 PM   #2
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replacing cast iron pipe


minium pitch for 3" and larger is 1/8" per foot and 1/4 per foot for anything smaller. if you pitch a line from a bathroom too much the water runs away from the waste and doesnt wash it down completely. In a kitchen sink bits of food would be left in the pipe when all the water drained away. its even worse if you have a disposal. i would run at the proper pitch then drop vertically when you need to. where does the vent go to now?? it would be nice if you could get the sink drain into the wall and vent it there.

vents can run a long way horizontally. just make sure to pitch the vent also. it should rise as it goes away from the drain line. if you tie the vent in in the area it is now use a t in the drain line and roll it up to at least a 45 degree angle or straight up if you can. it should be within 5 feet of the sink. double trapping a fixture has always been against code as far as i know. i wonder why they didnt tie the DW in at the KS.

no disadvantage to the vertical drop in pic 3.

you can run the pipe as close as you can get it. if you run pvc make sure to strap it good.


1-1/2 is the minium for a kitchen sink drain. the DW drains through a 5/8 hose anyway.
you can run 2 inch and use 1-1/2 for the vent and 1-1/2 for the drain and put a cleanout in the end.


leave as much cast iorn as you can. i would cut right close to where the wye comes off.


if you cut out the copper drains , cut off all the fittings and take them to the scrap yard. if they have fittings connected they give you the dirty copper price and not the clean copper price. make sure there are no brass fittings attatched either. they give you brass price if there are. post some pictures as you go along.

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Last edited by DannyT; 05-20-2011 at 10:29 PM.
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