# A stupid plumbing question



## DaveReading (10 Feb 2021)

Hopefully a question about stupid plumbing, rather than a stupid question about plumbing ...

The loo downstairs (35+ years old) had become almost impossible to flush, so I decided to replace the syphon with a more up-to-date one.

That involved removing the cistern, which was straightforward enough, but on refitting it and replacing the ancient, squashed flat doughnut with a new one I found that cistern was riding a cm or two higher than before. There was enough wiggle room in the fill pipe to reconnect it, but the overflow pipe would no longer reach the union on the bottom of the stack pipe, and I managed to break the drain pipe in trying to bring them together (I know, I know ...).

No problem, or so I thought - the necessary replacement pipe and a 90 degree elbow were only a couple of quid, and I got the hang of using solvent weld. I decided I might as well replace the overflow stack while I was at it.

That's where things started to go wrong. The original drain pipe was grey plastic, relatively thick-walled and 22 mm O/D. It was a snug fit inside the bottom of the stack pipe, which was made of a fairly flexible plastic such that a compression nut would produce a nice watertight union when nipped up (bearing in mind that it was only the overflow, so no real pressure).

The new stack pipe, although made of a less flexible plastic, has the same internal diameter, so the original 22 mm pipe would have been a snug fit and probably watertight, even allowing for the fact that the compression nut wouldn't really be compressing anything. Unfortunately, the standard nowadays for overflows is 21.5 mm O/D, which rattles around inside the stack pipe, and doing up the compression nut does nothing to make it watertight.

Leaving aside the fact that the plumbing industry seems to have standardised on two parts of an overflow system that don't fit together, can I ask if anyone else has encountered this problem and, if so, how did you resolve it ?


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## sheddy (10 Feb 2021)

Dunno. Can you post some photos ?


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## slowmotion (10 Feb 2021)

This might help.......

https://www.diynot.com/diy/threads/overflow-21-5mm-22mm.166635/


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## Andy_R (10 Feb 2021)

Yes, you can ask.


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## gbb (10 Feb 2021)

I replaced my cistern a few months ago, it was 50 years old'ish and thought it time to replace.
I had exactly the same problem...unable to connect the existing overflow pipe.

So I just wandered in the toilet to see how I overcame it....

I havnt !!!!!!

I must have put it off pending finding a solution....and forgot all about it. Theres a 1 inch gap between the cistern and the overflow pipe. I dont notice it because theres a shelf covers that side of the tank. Time for some thinking.


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## DaveReading (10 Feb 2021)

Thanks for the responses.

Here's a pic (not very informative) of the stand pipe: https://www.wickes.co.uk/Euroflo-By-Fluidmaster-Internal-Overflow-Stand-Pipe/p/150174#

Note that there's no reference to what diameter of pipe can be expected to fit it - doh ...


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## Randomnerd (10 Feb 2021)

IIRC an adapter can be had to sleeve inside / outside. McAlpine or Polypipe probs. Call your local Plumbcentre


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## Once a Wheeler (10 Feb 2021)

This may not match your problem but it is worth consideration. With a similar problem, I glued (epoxy resin — equivalent of Araldite) a short section of 20mm copper pipe into a plastic pipe. The copper pipe then took a standard compression fitting to continue the run. Hardly a standard or recommended procedure but it has withstood header-tank pressure (10 metre fall) for 15 years now. Plastic piping can be a nightmare. Good luck.


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## DaveReading (10 Feb 2021)

Randomnerd said:


> IIRC an adapter can be had to sleeve inside / outside. McAlpine or Polypipe probs. Call your local Plumbcentre



Just found this, which looks like it will do the trick: https://www.bes.co.uk/solvent-weld-overflow-pipe-straight-adaptor-215mm-11935/


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## newts (10 Feb 2021)

You could try a few wraps of PTFE tape around the pipe & then slide the nut up & tighten. Handtight should be sufficient as it's not holding back pressurised water.
External overflow pipes have been phased out over tha last 20 years in favour of internal that flow back into the pan via the siphon/flush valve. 
https://www.screwfix.com/p/flomasta-dual-flush-siphon-95mm/179fy 
If your replacement siphon has internal overflow capacity you can blank off the existing overflow.


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## figbat (11 Feb 2021)

This isn’t the imperial vs metric thing is it? Old one 7/8”, new one ‘nominally’ 22mm?


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## DaveReading (11 Feb 2021)

newts said:


> You could try a few wraps of PTFE tape around the pipe & then slide the nut up & tighten. Handtight should be sufficient as it's not holding back pressurised water.
> External overflow pipes have been phased out over tha last 20 years in favour of internal that flow back into the pan via the siphon/flush valve.
> https://www.screwfix.com/p/flomasta-dual-flush-siphon-95mm/179fy
> If your replacement siphon has internal overflow capacity you can blank off the existing overflow.



Thanks - yes, the new siphon does have internal overflow, which I'd never heard of before.

If I'd got my head around that earlier, I'd have saved myself a lot of bother.


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## newts (11 Feb 2021)

You can get an overflow blanking plug for the cistern. 
https://www.screwfix.com/p/flomasta...U-xH9NWV6bPndnpS4rIaAq1WEALw_wcB&gclsrc=aw.ds
Just check that the internal overflow is set at the correct height for your cistern & draining back into the pan. Blocking/removing the pipe to outside will stop cold air coming in & can reduce condensation.


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## DaveReading (11 Feb 2021)

newts said:


> You can get an overflow blanking plug for the cistern.
> https://www.screwfix.com/p/flomasta...U-xH9NWV6bPndnpS4rIaAq1WEALw_wcB&gclsrc=aw.ds
> Just check that the internal overflow is set at the correct height for your cistern & draining back into the pan. Blocking/removing the pipe to outside will stop cold air coming in & can reduce condensation.



Thanks, I'll bear that in mind when I replace the upstairs toilet syphon next.


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## rogerzilla (12 Feb 2021)

The standpipe in my upstairs chodbin cracked and needed replacing just before Christmas. It was allowing water to seep into the overflow and making the wall wet outside. Seems to be a relatively common problem, although I have no idea what causes it. Anyway, the overflow pipe and new standpipe were a good fit (or as good as they ever are; they are not designed to take pressure).


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## the snail (31 Mar 2021)

There are two kinds of waste pipe - solvent weld and push-fit and they are different sizes (and different types of plastic) so you need to buy the right fittings/pipe. Compression fittings should work with either type of pipe, so that's what you need to connect one type of pipe to the other


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