40mm basin waste

Possibly a "flexible waste pipe". Bend to suit, done.

(I have one in a shed, where I bend it into a trap when it's warm ,and straight to drain all water when it might freeze. Works...)

Thomas Prufer

Is there some reason why the trap can't be connected directly to the basin? If you can use a bottle trap, that will have a horizontal output, so you can connect a pipe to that to go back 15cm, then a 90 degree bend and then a piece of vertical pipe to connect up with the existing waste pipe using a 40/32 reducing connector.

I think you will find a bottle trap with a 32mm outlet will fit directly onto the basin waste and will probably project below the sink not much more than any pipe connections you will need to directly connect a pipe to it. Using such a bottle trap will mean simply completing the connection in the same 32mm pipe.

Richard

Is this the bit that pokes out the bottom of the basin that is the directly under the plug hole?

If so, any standard basin trap should screw onto this. A simple U bend type may be the best option. The connect a pipe to the output of that and appropriate fittings to get to your final 32 mm pipe.

Check if you need pushfit or solvent weld (if unsure go for compression "universal" fittings - they will seal on either).

Use swept bends rather than sharp elbows, and consider using a swept tee with a rodding eye in the unused end for one of the bends.

I should have explained this better in the first place!

I have fitted a new basin to an old piece of bathroom furniture. The furniture sticks out from the wall and is 9" deep. I need to keep the pipework within the furniture if possible.

The old trap is 7" tall, but with the new basin that's about an inch too tall. It sticks out at the bottom of the furniture, and besides looking odd it stops me closing the access panel.

So, I think you are right. I need an extra shallow trap with a a 40mm inlet and preferably a 32mm outlet. Then I can just finish the connection in 32mm pipe, and I don't need a converter.

Is it just me, or is the Screwfix website very bad at specifying both the inlet and the outlet connections on their traps?

Something like this is probably the answer. It does not have a water trap but uses a valve system to prevent sewer smells coming up the outlet.

Richard

PS

Just looked up BSP threads and 1 1/4” has an outside diameter of 41.9mm. Push a 32mm length of pipe into your outlet and if it fits without too much waggle then a 32mm fitting will do.

Richard

I'll check, but I think that must be the answer. I know that basin wastes are normally "32mm", but it's really confusing that I can't find anywhere that says the OD is around 40mm. OFC, that makes perfect sense if the 32mm pipe is going to fit inside.

I just need a 32mm trap, and I'll have a take-back-athon of the 40mm stuff. :)

Yes this is the problem of not going fully metric. You still have a lot of legacy imperial stuff still being produced in this case waste outlets but also tap tails which are also in BSP. I know the argument is that so much exists and you need to Be able to connect new to old but if you keep producing the imperial stuff you will never phase it out.

BTW have you considered the low profile trap I linked to it looks not much more than what you would have using standard waste fittings to link to either a bottle or P trap at the back of your cupboard?

As for finding out the OD just Google BSP threads and plenty of charts come up, of course you would need to know that the item has an imperial thread. In British plumbing generally anything pipework that attaches to a component by a thread is almost always imperial BSP (British Standard Pipe).

Richard

Also be careful that solvent weld pipe has a slightly different OD to push fit or compression fit pipe. I once made this mistake and had already cut the pipe before realising that the other fittings didn't seal :(

Just to add to the joy, I decided to buy a tool to cut the 32mm pipe, as it was a confined space and I needed to get it right first time. The cutter is described as a 35mm pipe cutter.

Why, for heavens sake?

Do not know what type you had in mind but something like this should do what you want and work up fairly tight up to a wall. There are cheaper but again it depends on how much room you have to manipulate them.

I splashed out on one of these: