Bad smell after changing bathroom sink

Adam · 9 Mar 2019 at 20:31

I've recently replaced my bathroom sink as the old one was cracked. During installing the new sink I extended both the copper pipes for hot/cold and also the waste pipe using 32mm and solvent weld. I also replaced the S trap with a good quality brand (McAlpine). There is now a very bad smell whenever the sink is used. It's the typical unpleasant drain smell.

It's strange as the sink didn't smell before it was changed but now it's not very nice at all. None of the other sinks in the house smell like this one either. It's not a bathroom that's used very often but nonetheless I'm keen to try and fix it.

Any ideas I can try?

Simon · 10 Mar 2019 at 00:14

Is the u bend full of water

Destination · 10 Mar 2019 at 11:03

Would seem that your water rap u bend isn't filling, so you're getting back smell.

niko · 10 Mar 2019 at 13:59

does it have a connected overflow, that's another area for smells

Psycho Sonny · 10 Mar 2019 at 14:15

maybe try a crap load of caustic soda or bleach?

Adam · 10 Mar 2019 at 15:47

Ok so the S bend was full of water when I took it apart which is a good sign.

https://imgur.com/a/gwy96Ez

In the image above I have highlighted where the S bend connects to the existing waste. The part that is connecting the 2 is not forming a tight seal, infact I can move the pipe with my hand. It almost seems that the S bend is too large for the existing waste which I know happens to be 32mm (as I bought some and used couplers and solvent weld to extend the pipe).

I'm 99% sure this is my problem and creating a proper seal will solve it. I just can't figure out why this McAlpine 32mm waste doesn't fit a 32mm pipe :confused:

DXP55 · 11 Mar 2019 at 09:03

did you put the rubber washer on the pipe and does the pipe push up into the trap -which it should.-

Fireskull · 11 Mar 2019 at 10:43

Yeah as above could be wrong and its below in the thread but it looks like its missing the rubber tapered washer on the end of the waste pipe, should look like the one in the top of this link, the tapered end should face upwards in your situation.
https://www.diy.com/departments/plumbsure-rubber-trap-washer-pack-of-3/178382_BQ.prd

Adam · 11 Mar 2019 at 12:40

Fireskull said:
Yeah as above could be wrong and its below in the thread but it looks like its missing the rubber tapered washer on the end of the waste pipe, should look like the one in the top of this link, the tapered end should face upwards in your situation.
https://www.diy.com/departments/plumbsure-rubber-trap-washer-pack-of-3/178382_BQ.prd

This might be what I'm missing and if that's the case I'm amazed it hasn't leaked! I checked the washers yesterday and have a large thin blue plastic washer, a smaller thin rubber washer but it looks like I'm missing the large thick black one. Thanks for the link. Naively I expected the S trap to come with everything I need but it seems like the washers are sold separately which is good to know.

I also went down another path where it seems that the diameters of the 32mm floplast solvent weld pipe is uncompatable with the McAlpine S trap unless you warm up the pipe so it can fit in to the trap securely. I found that information from here: https://www.ukclimbing.com/forums/off_belay/waste_trap_issue-657291 If that had been the case I was going to buy a floplast brand S trap and hope it would be a straight swap.

I'm more hopeful that the rubber washer could be the solution now, thanks so much!

DXP55 · 11 Mar 2019 at 13:18

You must make sure the pipe with nut on goes up into the S bend - I would have expected the S trap to come with the washers as well - One other thing - I am sure weld pipe is slightly different size to push fit pipe. - I fell for that once.