TOILET SIPHON AND 11/4" FLUSH PIPE:

[RONCHAM]

It's 120mm which divided by 3.142 gives o/d of 38mm near as dammit.

 

[RONCHAM]

Seems neither one nor the other? - I believe1¼" has o/d of 34mm and 1½" has o/d of 41mm?

 

[terryplumb]

Seems neither one nor the other? - I believe1¼" has o/d of 34mm and 1½" has o/d of 41mm?

It's 34mm and 40mm outside diameters For plumbing tubes that are not for Solvent welding.
Your flush pipe doesn't really need to be those sizes ,as long as it fits into the siphon and the flush cone it's somewhat irrelevant.

 

[RONCHAM]

Thanks again. I was a bit worried a quirky 50 years old cistern might have a small diameter outlet that wouldn't accept a modern (larger diameter) siphon. There might well be a flat washer inside the cistern on the base to seal the cistern but it's been backed up with a doughnut dollop of squishy sealant around it.

Regards.

 

[RONCHAM]

Hi Terry - sorry to bother you yet again but the plot thickens!

I dug out some (old) 1½" (38mm) and 1¼" (32mm) plastic pipe - I didn't think sizes have changed over the years but maybe they have? Circumferences are 136mm and 112mm whereas my existing pipe measures 120mm. But I'm now thinking my existing pipe is probably 1½".

However, I bought a Fluidmaster dual flush siphon. The siphon rubber sealing washer does not fit readily onto the 1½” pipe unless stretched and the coupling nut does not fit over it. Both are a loose and sloppy fit on the 1¼” (32mm) pipe?

Also, should the flush pipe fit inside the threaded siphon outlet or just butt up to it? Certainly the 1½” will not fit inside and if butted up to it there would be no gap for the sealing washer and it would be ineffective? The 1¼” pipe will easily enter inside the siphon outlet but then the sealing washer does not grip it tight enough to make a waterproof seal and the pipe can actually be pulled out.

So I'm very confused and will appreciate any further advice you or others can give.

Regards.

 

[RONCHAM]

(Actually I think I can answer one of my own questions! Looking at a YouTube video the flush pipe does fit a few inches inside the siphon outlet and although it's a loose fit, it's not an extremely sloppy fit and apparently the pipe coupling nut doesn't need to be especially tight).

 

[terryplumb]

You are confusing pipe sizes,with a flush pipe. They are not the same thing.
Yes the flush pipe goes inside the siphon tail about 20mm or so,but not that critical.
The siphon isn't for connection to either size pipe,it's for connecting to a flush pipe.
Does your new siphon fit into the cistern ,and does your flush pipe fit into the siphon ? Forget the bits of pipe you have which are irrelevant.

 

[Justin Passing]

One of these: ?

BES.co.uk | Next Day Delivery On 15,000 + Plumbing Supplies

Order Macdee Extended Flushpipe - 2" to 1.1/2" and other toilet accessories online at BES.co.uk. Low Prices, Free Next Day Delivery Available, 15k Plus Products in stock. P/N: 20028.

www.bes.co.uk

There are several types of cone - different materials which accommodate a variety of sizes.
This takes 38 not 40 - see comments

BES.co.uk | Next Day Delivery On 15,000 + Plumbing Supplies

Cisterns and Accessories / Push In Connector - PN: 11205 - Order Gas and Plumbing Supplies online at BES.co.uk. Low Prices, Free Next Day Delivery Available, 15k Plus Products in stock

www.bes.co.uk

BES.co.uk | Next Day Delivery On 15,000 + Plumbing Supplies

Cisterns and Accessories / Universal Connector - PN: 11206 - Order Gas and Plumbing Supplies online at BES.co.uk. Low Prices, Free Next Day Delivery Available, 15k Plus Products in stock

www.bes.co.uk

 

[RONCHAM]

Thanks yet again for your comprehensive reply. Of course, you're dead right and I've been wrong on a couple of things. I did a bit of research since I posted earlier and see that SFix do a 38mm dia. flush pipe (I presume outside dia.) which would be perfect - the internal diameter of the siphon tube is about 42mm. Coincidentally 38mm is the outside dia. of my existing "mystery" flush pipe which is where I came in! - it will probably be reusable. And you're very likely right that one or two new seals would also sort the problem. One day soon I may be flushed with success!
Thanks again - it's very good of you to share your knowledge.

Regards.