Limited options for adding a boss to 90mm cast iron stack

[c.raab]

Hello,

I have the exact same issue as this chap had 4 years ago, however I am unable to post on that thread and no solution was ever arrived at (Cast Iron Boss for 40mm waste - https://www.plumbersforums.net/threads/cast-iron-boss-for-40mm-waste.89358/). I have already read a lot of threads on this forum, scoured the WWW for hours & spoken to plumbers merchants and even called McAlpine sales.

AIM: I have a combined rainwater and kitchen waste stack made of 90mm cast iron that I am adding an additional sink to.

The issue is that nobody appears to make a strap-on boss for a 90mm pipe. There are plenty of options for 110mm and 82mm. The only product I can find that might work is the McAlpine BOSS90TCAST-BL, however it isn't ideal as you are reduced to 22mm ID. McAlpine said it wouldn't work, but I think they have to say that, I can't see why the water wouldn't flow through, the sink would just drain a bit slowly.

The plumbers merchant said I might be able to use the McAlpine BOSSCONN82T-BL however he wasn't sure how good it would work on a 90mm pipe. McAlpine sales again flat out said it wouldn't work.

Does anyone know of any alternatives I might have missed? Any suggestions or advice would be appreciated.
Thank you
Rab

 

[c.raab]

anybody?? Are there just no alternatives or did I explain something wrong?

 

[ShaunCorbs]

Two Piece Cast Iron Soil Pipe Boss Connector | McAlpine Plumbing

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

mcalpineplumbing.com

??

 

[c.raab]

Hi Shawn
Thanks for the reply. That is indeed the only part that I can find which is a possible solution. I referenced it in my original post:

The only product I can find that might work is the McAlpine BOSS90TCAST-BL, however it isn't ideal as you are reduced to 22mm ID. McAlpine said it wouldn't work, but I think they have to say that, I can't see why the water wouldn't flow through, the sink would just drain a bit slowly.​

I am an engineer but not a plumber. Would the reduction in ID from a 40mm waste to 22mm be an issue?
Thanks.

 

[ShaunCorbs]

Basin ? Or kitchen sink

Two Piece Cast Iron Soil Pipe Boss Connector | McAlpine Plumbing

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

mcalpineplumbing.com

This would work but wouldn’t look the best as there would be a 5ish mm gap either side but the rubber part would seal

 

[moonlight]

Is the stack internal or external? If its external might be worth considering an upgrade.

 

[king of pipes]

Saint Gobain timesaver range do a boss pipe adaptor and clamps to suit , there is a strap on but its for 100mm ??? Kop