Phantom drain smell

[OneHandFlapping]

For the last 6 months we've had this occasional terrible smell - always noticeable in the kitchen first. It's obviously drains, but we can't pin the smell onto any particular household event - sometimes it appears after someone has had a shower, or let out the bath, but othe times there is no link to any watery stuff in the house.

We had the kitchen extended about 18 months ago. There were no problems before that, but the problem didn't start immediately after the extension was completed either.

We've had all the external drain covers off, and the drains are not blocked. We've sniffed all along the soil pipes, and there is no leak or smell near them. We are at a loss as to how to track it down.

Apart from exorcism, has anyone got any ideas?

tell me where the wastes for the washing machine and dishwasher are plumbed in.

Does anybody tip cooking fat down the sink?

Does the ceiling (under the bathroom) smell?

Is there a plumbing duct in the corner?

Hi PigletJohn.

The waste from the dishwasher goes into the drain from the kitchen sink, below the plug hole and above the Ubend. Inevitably a small amount of cooking fat goes down the sink, although there haven't been any blockages.

The waste from the washing machine hooks into a stand pipe in the utility room, but the smell never seems to come from the utility room.

The ceiling doesn't smell, nor are there any stains. The whole run of all the upstairs soil pipes is accessible, and I can't see any leaks, nor identify any smell around the soil pipes, even when it is eye watering in the kitchen.

What's a plumbing duct?

We had something smelly going on with our house too, we found out the main waste pipe was broken where another pipe was attatched to it and waste from the bath, toilet, washing machine, dishwashers, sinks, everything was gathering in a nice puddle under our house!

How did you locate the source of your smell ClaimedByMe? TBH that's the sort of thing I'm worried by - especially as an old drain was supposedly sealed off under the extension.

When the dishwasher waste hose attaches to the sink waste, it needs to be curved up so that the top of the curve is higher than the water level in the sink when full (e.g. fix it to the underside of the worktop). Otherwise dirty sink water can run down the hose into the appliance (the same can happen with washing machines). Stand pipes do not suffer from this.

That was just an idea and may not be your problem. However I am considering the possibility that there is a partial obstruction in the soil pipe, causing waste to back up and drain away slowly. If you had an extension built they may have altered or extended the underground pipes, and there might be a manhole cover or a gully that was formerly outside the house and is now under the floor. If concrete has been laid it will be very difficult to get at, but if wood, a section could be taken up (for example in the empty space of a kitchen corner, or under a unit or appliance) to have a look or a sniff.

By plumbing duct, I mean (in a modern house where the soil pipe is not on the outside of the hose) where the pipes run down from the bathroom, usually in a corner and usually boxed in. If there is a leaking joint you can usually detect damp or smell inside this boxed in duct.

If you have any inspection covers/manholes it is always useful to open them up and see if water flows freely when the bathplug comes out, sinks are drained, WCs flushed.

You are very knowledgeable PigletJohn!

There isn't a loop in the dishwasher outlet - it would be easy enough to detach it and loop it over another pipe though. There is no smell from inside the dishwasher ever though, so I'm not sure how it would be escaping.

No smell around boxed in soil pipe.

New drains were laid round the whole new part of the house, and existing and new waste pipes attached to them. There was a manhole cover under what's now the kitchen, but that was supposedly sealed. Definitely nothing is directly attached to it now. We'd need a bit of proof before we tore up our lovely tiled floor, underfloor heating and at least 6 inches of concrete - not sure how a smell would get through all that tbh.

I will check whether bathwater flow freely down the drains. So far we've just checked that there is no standing water anywhere in the drain system. How would the smell get into the house frome here anyway?

The smell appears every few days. Sometimes we can go a few weeks without it appearing. There is no rhyme or reason to it.

Does it smell a bit gassy? We had a sporadic gassy smell for a year and drains was one of my worries, but it turned out to be rats in the cavity walls between us and our neighbours.

Definitely drainey. It comes for about half an hour and either disappears or fries our smell receptors so we don't notice it after that.

There can be a fine line between drainy and gassy.

The company putting in our new central heating found it when they were under the floor putting in new pipes, we got out a company to fix it, clean up the mess and put lime down to elminate any smells!

Can you get under the floor anywhere to look under?

We would smell it in the hallway as we came in the front door as there is a vent in the floor there for the heating pipes which is the opposite side of the house the leak was at which was under the kitchen floor.

We had a phantom drains smell in our first floor bathroom.

It turned out that when the previous owners had redone the bathroom, they had not got rid of the old pipe to where the old sink had been. So that leftover pipe was still connected to the main soil pipe but was connected to nothing at the other end (the other end was just open under our floorboards). Every time someone flushed water on the top floor, this caused gases to flow from the soil pipe out of the open end of the leftover pipe.

We only worked this out because we realised there were 4 small pipes on the outside wall of the bathroom (joining on to the main soil pipes) but only 3 things that needed small pipes (sink bath and shower).

Any chance you could have something similar? Has the layout been rejigged at any stage? Can you work out what all the outside pipes are for?