Struggling to find an sink trap adapter.. Any ideas?

[FuerteStu]

Got an 1.5" basin sink waste into 1.75" trap. 

Was thinking such a simple adapter would be easy to find, but alas I'm only finding the wrong sizes, or reverse threads (female to male instead of male to female etc) 

 

I've already got 1.75"pipe and AAV coming up under the sink.. Would it just be better to get another trap and reduce it there? Or can anyone find something like the macalpine T16 that's actually the right size?

[Marvin]

Possibly:

 

https://getplumb.co.uk/products/mcalpine-1-50-x-1-75-bsp-coupling?

 

 

 

[FuerteStu]

Very possible! 

 

Just concerned about the amount of thread on the 1.75" side.. 

[Marvin]

7 minutes ago, FuerteStu said:

Very possible! 

 

Just concerned about the amount of thread on the 1.75" side.. 

Silicone it in using Dow 785 white - (allow 24 hours to dry whilst not fitted to sink and in the dry and warm)

[FuerteStu]

On 27/12/2025 at 12:25, Marvin said:

Possibly:

 

https://getplumb.co.uk/products/mcalpine-1-50-x-1-75-bsp-coupling?

 

 

 

Update.. Ordered from these guys, after a week I got a call saying they don't have it and they would refund. 

 

Ordered instead from 'plumbing supplies delivered' and after 2 weeks it's arrived and they've sent the T12 instead of T12F so the threads are the wrong way round and it's useless. (I paid for a delivery upgrade to get it fast too) 

 

I've come to the conclusion that all plumbing suppliers are utterly useless and it looks like I'm throwing away the 40mm pipework and AAV already fitted under the sink and doing it in 32mm.

 

After a month of messing around 🤣🤣😭😭

[Nickfromwales]

Just reduce 40>32mm at the point these two meet, and fit a smaller trap?
 

That’s what I do, as I never run long lengths of 32mm pipe for basins any more, always 40mm and then reduce at the bend where it turns from vertical to horizontal. I use a 40mm 90° bend with a 40>32mm reducer glued into the bend, and then a short piece of 32mm to an 1.5” trap. 
 

Simples. 
 

You can even just buy an anti-siphon 1.5” trap. 

[FuerteStu]

That's what I'll be doing.

 

What's so frustrating is that it shouldn't be a big deal to tell someone they don't have it, or send it the right one. I could have adaptated and fitted this a month ago. 

[Nickfromwales]

3 hours ago, FuerteStu said:

That's what I'll be doing.

 

What's so frustrating is that it shouldn't be a big deal to tell someone they don't have it, or send it the right one. I could have adaptated and fitted this a month ago. 

Respectfully, nobody puts a 40mm trap on a 32mm sink.

 

Agreed, they should have just said no, but sales always starts with a “yes”, and the let down follows after a lot of laborious provocation.

[FuerteStu]

I didn't know it was a thing that wasn't done. Considering most of the wholesalers listed it as an adapter on their websites I assumed it would be a common connection and not an issue. The 32mm trap in the downstairs bathroom gets clogged up regularly, I figured keeping it 40 would be better

Mcalpine is a brand leader, standard. It's their product

 

It wasn't until I visited local places and just got shrugs that I looked online and nobody had it in stock. 

And those that said they did screwed me around. 

The mcalpine store on amazon doesn't even stock it.. Yet nowhere does it say its been discontinued. 

 

 

[Nickfromwales]

Scrap the bigger trap, move to a P or bottle trap, enjoy life with a job well done.

 

Traps are easy to ‘self clean’, so it’s no biggy.