help with the boss please

28 Jun 2005
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United Kingdom
Hi I am helping my mate put in his new toilet. It has a saniflow so the outlet is 32mm and we have to join that to the main stack which I believe is cast iron.

As I understand it we need a boss I see these have two little lumps on them which one of the guys at the DIY store told me you cut the stack hole big enough to encompass these lumps as I call them, not sure what size hole that should be, it looks like it will have to bigger than the 32mm front opening, but have not measured that bit yet.

Anyway apart from that, all the DIY stores seem to have is solvent weld types. Surely if we are joining to cast iron we will need a different kind ( which it seems DIY stores do not keep) or is it possible to use the solvent type anyway? The guy in the store said he thinks you can get ones for cast iron that will take the 32mm plastic pipe but they are really expensive, £35 or something, is this right? In that case definitely is it possible to use the solvent weld type obviously not with the solvent but maybe with silicon or is that not possible, the guy did mention something about the cast iron being bigger than plastic stacks as well.

Some guidance and help would be appreciated please.
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A strap boss will do the trick, although drilling the CI will be a pig to do. It's the straps on the boss that'll hold it on.
A strap boss will do the trick, although drilling the CI will be a pig to do. It's the straps on the boss that'll hold it on.

So are you saying the solvent weld type will be ok to use? Should I just use a bit of fernox leak sealer/ silicon if so?

The guy sold me a 32mm boss solvent weld type to try which has a strap with a bolt, is that the right one to do it this way?

Any tips on drilling the CI, I heard it can be tough?
Cast iron can have a hard 'skin' that can quickly blunt cutters, but it is usually only a few thou thick, and the rest usually cuts quite easily. For one hole I would consider chain drilling with about a 1/4" drill and finishing with a half-round file.

Chain drilling = drilling a circle of small holes one hole diameter apart around the piece you want to remove, then cutting out any thin webs left between the holes.
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Happy - it looks like this:

Follow TicklyT's advice for hole but care needed at end of drilling so the waste disk in the middle doesn't drop into the pipe. Solution - drill small hole in center of the waste disk before you start chain drilling, insert a self-tapping screw, fix wire or string to the screw and the other end around the pipe to form a lanyard so if it does drop you can fish it out. Also, buy a few decent twist drills, 'cos you will snap some.

Seal with silicon.

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