Smell from sink overflow

Last week, our cloakroom (spare loo) developed a smell - a dampy mouldy smell.
Investigation tracked it to the overflow slot in the handbasin ????
Working on the premise the sink is rarely used, I disassembled the waste (bottle) trap, which was gooed up with a grey slime (which *was* the smell). Cleaned it all up, and proceeded to put the plug in, and put a tap on pouring a mixture of bleach and hot water downthe overflow.
All well for 6 days.
Now the smell is back - same place, but worse then ever.
The actual plumbing for the waste starts in the next room (the utility) where the washing machine discharges into a U-bended inlet. That runs into the cloakroom, where the outlet of the waste runs into it. From there it runs into the waste connector for the WC (which was made with a connector for waste.
So was my cleaning of the overflow in the basin not thorough enough, or could something else be combining to allow the smell into the room ?
Does it have any bearing that the basin is practically never used (just the 2 of us nowadays) ?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 21/05/17 11:36, Jethro_uk wrote:

check that traps are not being sucked dry.
You may have air admittance valves that have failed also
--
"When one man dies it's a tragedy. When thousands die it's statistics."

Josef Stalin
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

We have the same problem, although three of us here. I have mentioned before that this house was once a B&B, and there are more sanitary fittings than we will ever use. I find it surprising, how quickly the water in various U bends will evaporate, just enough to let a pong through, so try to remember to flush toilets and run water regularly. My nose tells me when I forget.
--
Graeme

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 21/05/2017 11:36, Jethro_uk wrote:

I'd check 2 things. One being that the water in the trap has just evaporated. I look after a small office block and one suite was empty for a few months. In hot weather a pong had started within a week. I used to flush the WCs & run the taps every week.
Secondly, it's possible that the WM emptying or the WC flushing is syphoning the water out of the trap. I think there is a valve you can install.
Dave The Medway Handyman
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 21 May 2017 14:50:18 +0100, "Phil L"

+1
We had a similar problem with our kitchen sink. I would appear that some of the bacteria that accumulate in these obscure places are difficult to shift in their entirety, and if a few bugs get left behind they soon multiply in the slime that accumulates there, and start smelling. It was only frequent and generous spraying of dilute bleach into the overflow of our sink that eventually got rid of the problem.
--

Chris

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 21 May 2017 10:36:01 +0000, Jethro_uk wrote:

Thanks for all replies ... I'll try the daily bleach routine for starters. Hadn't thought that the loo could be siphoning the bottle trap ... also have to maybe run the tap daily to ensure the trap stays full.
If I don't repost, it'll have been solved !
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snip

You can get bottle traps with an integral anti-syphon valve, which would be a good idea if the trap empties in less than a week or so.
--

Roger Hayter

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
     snipped-for-privacy@hayter.org (Roger Hayter) writes:

Here's an example: https://www.bes.co.uk/polypipe-1-1-4in-32-mm-with-3in-75-mm-seal-anti-syphon
If syphoning is the cause, it will empty the trap with one flush of the loo, or one pump-out of the washing machine, or whatever other drain causes it.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Or, if the waste outlet is lower:
https://www.bes.co.uk/polypipe-1-1-4in-32-mm-with-3in-75-mm-seal-anti-syphon-with-adjustable-telescopic-inlet
--

Roger Hayter

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Can I just suggest checking the manhole outside before doing anything complicated. It probably isn't a blockage, but it's easy to check.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 22 May 2017 15:36:07 +0100, GB wrote:

As you say, easily checked, and all OK :)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 22/05/2017 16:13, Jethro_uk wrote:

:p
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

'nother method to clean the overflow is to use shaving foam from a can. Squirt in, possibly using a bit of tubing if handy, let sit overnight, rinse out.
It sticks in place much longer than other cleaners, and tends to shift stuff that needs a good long soak.
Thomas Prufer
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.