Drilling a cast iron soil pipe

[endecotp]

Dear Experts,

How hard is it to drill a cast iron soil pipe? This is to connect a condensate drain from a new boiler. The options are:

(1) Outside to a cast iron rainwater pipe.
(2) Inside to a cast iron soil pipe (which involves opening up some studwork). (I'm in a ground floor flat, it serves 3 flats above me.)
(3) Pump, running to a kitchen sink drain - which would involve poking pipes under floorboards and behind kitchen units.

The aspect that is totally unknown to me is drilling into a cast iron pipe, in order to fit a boss for the new 22mm pipe, for (1) or (2). I've had a heating engineer visit to look at the boiler installation generally and he seemed unenthusiastic about it. Is there a danger of breaking the pipe, for example?

Please share your thoughts.

 

[Mottie]

What does the heating engineer recommend?

 

[endecotp]

What does the heating engineer recommend?

He seems to like the idea of the pump, but he’s never tried to feed pipes under my kitchen floor, nor deal with the sink drain when it gets blocked and needs to be vacuumed. I think I’m going to ask him to route it to the soil stack. We only spoke about it briefly. I’m just looking for any experiences you can share about drilling cast iron.

 

[Mottie]

The lower part of my soil stack is cast, the upper half is some sort of cement/asbestos material. I drilled into my upper half where it went through the roof to fit a boss as my boiler was in the loft. It was a job and a half!

 

[denso13]

I’m just looking for any experiences you can share about drilling cast iron.

Not too difficult with a decent hole cutter, go slow.

 

[Razor900]

Can you not break into the kitchen sink waste just before it enters the stack? Don't do it if the pipe is copper

 

[Odds]

Not too difficult with a decent hole cutter, go slow.

Adding plenty of lubricant as you go, i'd add.

Also, check the area before you start to see if any cracks lurk beneath the surface.

 

[endecotp]

Can you not break into the kitchen sink waste just before it enters the stack?

No; the sink is at the far side of the kitchen, and the pipe disappears into the wall and goes god-knows-where. The stack I’m considering is nearer the boiler; it comes from upstairs and has no existing connections on this floor.

Don't do it if the pipe is copper

One of the easier routes under the kitchen floor would be to re-use a redundant CH pipe - except that it’s copper, which I guess you can’t put acidic condensate down, right?

 

[Madrab]

which I guess you can’t put acidic condensate down, right?

Right

 

[endecotp]

I’ve just found that McAlpine have bosses for cast iron specifically for condensate that only require a 22mm hole to be drilled:

Two Piece Cast Iron Soil Pipe Boss Connector

Upgrade your soil pipe connections with the Two Piece Cast Iron Soil Pipe Boss Connector, ensuring durability and efficient water flow.

mcalpineplumbing.com

This feels somewhat less “exciting” than drilling a 40mm hole through the cast iron!

 

[denso13]

It shouldn't really be 22mm if external, the manufacturer's instructions will clarify

 

[endecotp]

It shouldn't really be 22mm if external, the manufacturer's instructions will clarify

Right, yes, I have a choice of two cast iron pipes, one internal and one external.

Note the McAlpine part linked above actually takes a 32 or 40mm waste pipe, which narrows to go into the cast. I don’t know what the boiler manufacturers would think about that, in terms of freezing risk.

 

[endecotp]

I found someone with a bit of rusty old pipe in his garden that he was happy for me to take away, and I’ve been practicing;

That’s a cheapo Erbauer hole saw, in my old corded drill that I’ve not used for years, set to speed 2. Success; it cuts reasonably quickly with not much force applied and no catastrophic failure.

So do I dare to drill my actual soil pipe???

Adding plenty of lubricant as you go, i'd add.

I’ve done this dry; what exactly would you use for lubrication?

 

[Madrab]

I’ve done this dry; what exactly would you use for lubrication?

You can get cutting oil but a medium grade mineral oil will do, 3-in-1 is great for that. Another option is to cool it while cutting and that will save the cutting head too - water in a squirty bottle will do the job.
If it's cutting well dry though then great, all the oil/water does is saves the segments from wearing too quickly.

 

[dilalio]

And you can't discharge condensate into a cast iron stack either!