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 Connecting Plastic drain pipe to Cast Iron
Author: DJH (NY)

I am trying to sell a home for someone that does not live in the same area as I do. In order to pass inspection for the septic system, I have to run a PVC plastic drain line from a clothes washer in the basement, a distance of about 20 ft. into a vertical cast iron pipe. The height of the washer outlet should allow me to get enough slope from the washer to the drain pipe. The vertical pipe connects to the horizontal cast iron pipe which goes through the wall and into the septic system.

What is the best way to drill the access hole into the cast iron pipe, and what type of a connector should I use so that the connection does not leak?

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 Re: Connecting Plastic drain pipe to Cast Iron
Author: davefoc (CA)

caveat: I'm not a plumber.

What you are proposing is a maximally mickey mouse solution.

The proper way the do this is to cut a section of the cast iron pipe out, install the appropriate Tee fitting (ABS or PVC is ok) using no-hubs and then attach the drain pipe you want to add to the new T.

There are a few things you need to know about to accomplish this task.

1. Cutting cast iron pipe

There's quite a bit of discussion on this in various places in this forum. Grinders with cutting blades, reciprocating saws and special cast iron pipe cutting tool can be used.

2. Selecting the proper T.
A sani-tee is probably required if I understand the problem. Sani-tees are designed to reduce the possibility of siphon action draining a p-trap

3. A p trap is probably required some place near where you connect the washing machine drain. Connecting the washing machine is usually done be putting a rubber drain hose from the washing machine into the a vertical pipe that is attached to the p trap.

4. Maintaining the appropriate slope.



However, by coincidence, I helped a buddy fix an installation where somebody had connected a shower drain into a four inch cast iron plumbing stack by just drilling a hole in the cast iron pipe. I don't think it's a very reliable approach but we used a gray epoxy glue that was designed for plumbing work to seal the hole where the drain pipe entered the plumbing stack.



Edited 1 times.

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 Re: Connecting Plastic drain pipe to Cast Iron
Author: hj (AZ)

What kind of inspection, or inspector, would require an improper connection such as that?

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 Re: Connecting Plastic drain pipe to Cast Iron
Author: h2opro (NE)

Venting the laundry is an issue as well...your p-trap will be above grade, which (but probably not) could lead to syphonage..especially since it sounds like your connecting it near the bottom of your stack. You could be in luck though if you have a basement bathroom near the laundry.

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 Re: Connecting Plastic drain pipe to Cast Iron
Author: davefoc (CA)

I thought of the venting issues after I made my post.

Connecting the washing machine drain like this would constitute a wet vent. I am not quite sure when that is allowed by code, but I think there are restrictions when the drains are between floors. This might be a minor issue but I was wondering if an installation like this would pass inspection.

There is also an issue of the maximum slope of the drain line before the vent. I think there is some code restrictions on the maximum slope.

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 Re: Connecting Plastic drain pipe to Cast Iron
Author: redwood (CT)

20' is no vent! Also with fixtures above using that stack a separate vent would be required even if it was close enough to the stack.

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 Re: Connecting Plastic drain pipe to Cast Iron
Author: davefoc (CA)

redwood,
I am sorry but I am not quite knowledgeable enough to understand your post and I would like to.

Are you saying that there is a limit on how far the horizontal pipe after a trap can flow before a vent is required and twenty feet is much more than that limit? So that a horizontal pipe that flows twenty fee is essentially the same as not having a vent. My apologies, this is an area where I might not know enough to ask an intelligent question.

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 Re: Connecting Plastic drain pipe to Cast Iron
Author: redwood (CT)

Yes that is exactly what I'm saying. Also if that stack has fixtures from above draining into it, a separate vent needs to be run. wet venting between floors is a no-no.

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 Re: Connecting Plastic drain pipe to Cast Iron
Author: h2opro (NE)

exactly....like I said..if you have a basement bathroom downstairs...there is hope..you could vent the laundry and tie it in with the bathroom vent...the fixtures only need to be on the same level..or floor...the vent serving those fixtures can then be tied together at a height no lower than 6" above the highest fixture...typically 42" high..if applicable...or higher if need be....just no lower.

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