Connecting New WC Pan To Old Cast Iron Soil Pipe

[Deluks]

Out toilet has the same height issue.
It's a 1990's pan, using an offset connector onto a straight plastic extension piece, which has been cut down to make up the distance, into the CI pipe.
It does mean the toilet is flushing uphill a tiny bit, but the cistern has a big capacity, before the water saving ones were a thing.

That CI stack looks really neat, get some paint on it!

The extra work and expense involved in that install is surely worth it, that pipework has probably outlived the original guys that installed it.
Can you say the same about lightweight plastic cr@p?

 

[Scally-Ho]

"The extra work and expense involved in that install is surely worth it, that pipework has probably outlived the original guys that installed it.
Can you say the same about lightweight plastic cr@p?"

Extra work is an understatement. Not just the cutting and nailing, but yarning up and well compressing it before pouring the molten lead takes some effort, and then of course there's the caulking irons on the set lead to smack the lead up tight into the collar without cracking it. After all that when the air test reveals a sand blow hole somewhere in the cast, there is the bitumen brush applied to seal that crafty pin hole. Give me a decent run of well-made plastic any day; but be careful, there some rough brands of plastic out there I wouldn't scrape my boots with.

 

[ReganAndCarter]

"There is a low level pan called a Twyford classic that seem to have a P trap. Wondering if the outlet spigot may be higher as I'm guessing this pan is aimed at older installs. The spigot height (floor to centre line of spigot) is 190mm in the link below. Will have to have a measure".

Yes, some P traps do vary from manufacturer to manufacturer and some measure at 185mm. But that is doable with that length of CI protruding in your photo. Cut the CI close to the wall and with modern connector fittings, you will still have a fall from a 185mm pan outlet. The Multiquik range have got me out of trouble more times that I can remember over the years

Thanks for your reply. Do you recommend Multikwik pan connectors rather than something like a McAlpine in this case? Do they seal better, especially if there is a height difference between old and new pan spigots?

Also which size connector would I need? Says 4" on CI pipe, is this external or internal diameter?

 

[ReganAndCarter]

Out toilet has the same height issue.
It's a 1990's pan, using an offset connector onto a straight plastic extension piece, which has been cut down to make up the distance, into the CI pipe.
It does mean the toilet is flushing uphill a tiny bit, but the cistern has a big capacity, before the water saving ones were a thing.

That CI stack looks really neat, get some paint on it!

The extra work and expense involved in that install is surely worth it, that pipework has probably outlived the original guys that installed it.
Can you say the same about lightweight plastic cr@p?

Yes, stack will benefit from some paint eventually so it doesn't look so weather beaten.

I take it my idea of raising new pan slightly on some ply underneath to get more fall for it's lower spigit it is a non-starter? The old pan sits on the floorboards, but there is hardboard sheet laid around it then tiles on top of the hardboard. So raising pan up a bit on some thinish ply wouldn't be too obvious - not that the place is a palace anyway.

 

[opps]

As an aside... someone here once explained why cast iron soil pipes often had cracked paint finishes.

It turns out that day in the day, the internal surfaces of the case iron guttering were painted with a bitumen based paint. Sometimes, people would, accidentally paint the downpipes with the same paint.

If you plan to paint the soil pipe. I would recommend something like Hammerite smooth. The prep will be lower than grey undercoat and black gloss. Beg/borrow/steal some cellulose thinners to clean the brush- but treat the brush as a throw away at the end of the job. ie spenda fiver rather than 15 quid on the brush.

 

[Deluks]

Yes, stack will benefit from some paint eventually so it doesn't look so weather beaten.

I take it my idea of raising new pan slightly on some ply underneath to get more fall for it's lower spigit it is a non-starter? The old pan sits on the floorboards, but there is hardboard sheet laid around it then tiles on top of the hardboard. So raising pan up a bit on some thinish ply wouldn't be too obvious - not that the place is a palace anyway.

That's doable. I did similar for someone a few years ago, but used 2 layers of 12mm cement board to raise it up a bit. It looked a bit odd but the following year they had a refurb and it all got ripped out, new plastic soil pipe installed.

 

[Scally-Ho]

Thanks for your reply. Do you recommend Multikwik pan connectors rather than something like a McAlpine in this case? Do they seal better, especially if there is a height difference between old and new pan spigots?

Also which size connector would I need? Says 4" on CI pipe, is this external or internal diameter?

With good tolerance plastic mouldings on offer today, there is not much between any of them except perhaps the lower cost Aquaflow. Aquaflow do seem to be poorly finished at times, but it's probably all down to luck. They all do the job and with their flexible plastic seals, all allow a bit of shoving here and there to get the pan into the desired position. Try to avoid those DIY type elephant's trunk style of flexible extenders as they are not what I call a proper job. Don't worry about that 4" as the sealing fins of the plastic connector will ensure a good seal, but make sure that the inside of the CI is as clean as you can scrape it without too much fuss and all should be well

 

[ReganAndCarter]

Just want to check one thing, as I'm about to order the bits to do this job this weekend. Which type of pan do I need? P trap or horizontal outlet? I'm going to get a Twyford Classic low level pan. To recap, it's a 64 year old installation, upstairs. Pan discharges into a horizontal 4" cast iron pipe that goes through wall to CI stack outside. I will be using a McAlpine MAC-1 straight pan connector to join new pan to old CI pipe.

Unfortunately, the pan to CI pipe socket joint is swathed in Denso tape, so I can't make out if pan outlet curves downwards as a P trap, or is horizontal. Unfortunately, can't remove the tape to have a look otherwise will leak a lot.

Also, looking at my photo below, is the the outlet on the P trap toilet bigger bore than the outlet on the horizontal version? Or is the camera making it look that way? Any advice apreciated before I order the wrong version.

Twyford Classic.jpg

• ReganAndCarter
• 3 Jun 2025

DSC01923.JPG

• ReganAndCarter
• 13 May 2025

 

[ReganAndCarter]

I'd also (if you haven't already) offer the new pan (or the dimensions at least) to what you have already, the old P Trap outlets don't always line up with the modern Horizontal Outlets, so may need to cut the soil pipe further back to the wall and use a pan connector extension (or similar method) to extend the pipe back and get the right height.

Reading Hugh's advice again, looks like the old pan will be a p trap. So hopefully I buy the P trap version of the Twyford Classic pan as opposed to the horizontal version - new pan outlet should be correct angle and height for the existing CI pipe. Hopefully..........

 

[Hugh Jaleak]

Given the era the current pan was installed, I'd wager it'll be a P Trap. The usual issue is trying to mate a HO pan with a soil pipe that's be fitted to suit a P Trap, and finding you're asking the proverbial to run uphill as the HO is lower than the soil pipe spigot.

 

[ReganAndCarter]

Given the era the current pan was installed, I'd wager it'll be a P Trap. The usual issue is trying to mate a HO pan with a soil pipe that's be fitted to suit a P Trap, and finding you're asking the proverbial to run uphill as the HO is lower than the soil pipe spigot.

Before I read your post I took the risk and ordered the P trap version from Travis Perkins. P trap would make sense to suit the rising angle of the CI pipe as it comes out from the wall to meet the pan. In the unlikely event of it being horizontal outlet, they also have this version on the shelf at my local branch, so no problem to exchange the pan. Hoping the old and new P trap spigots are the same height from floor so no ply needed under base of pan.

Will see how it goes. Thanks to you and everyone else who helped out with advice.