smelly drain - help please

[mcs135]

I have a drain outside the kitchen door that sometimes gives off a real stink. The smell is associated with the outlets from the upstairs bathroom (sink, shower & bath). The upstairs sink, shower and bath outlet pipes each feed separately into a small 'hopper' on the outside wall 3 meters above the ground. This single pipe then leads down to a drain at ground level, where the dishwasher and kitchen sink outlets feed into. there is a U-bend in the drain that stops smells coming from the sewer. I have cleared this U-bend and drain thoroughly, but the smell persists.
From reading other topics I think that it cannot be anything to do with vents (I may be wrong), but is more likely to be dirty pipes.

Am I right, or is it something else?

If it is the pipes (as they run under floorboards I don't want to have to take up the flooring) what's the best method of cleaning them? Are there special cleaning tools for this?

 

[powell30]

Where does the smell come from.....do you smell it inside/outside? if inside what rooms.......if you have cleaned out the kitchen gully trap does water seal the bottom ie prevents backdrafts up the line?? A hopper is unlikely to smell as water doesn't collect there but more info would help

 

[mcs135]

Thanks for responding powell30.

The smell is coming from the drain. There is a good level of water in there to prevent smells coming from the sewer.

Does this help you answer my problem?

 

[Softus]

There is a good level of water in there to prevent smells coming from the sewer.

Water won't prevent smells from the sewer if there is positive pressure beyond your gully.

Have you lifted the inspection chamber lid yet?

 

[mcs135]

I have two inspection chambers before it reaches the main sewer, and both are clear.

 

[powell30]

MCS have you done what i asked you to in the other thread you posted on this subject??......smells can't 'travel' past a water seal. Either the seal is being breached or the water is rancid and your telling us the gully is clean and water sweet...(within reason)......do what i ask and report back....then we can reassess.

 

[Softus]

......smells can't 'travel' past a water seal.

This is not a true statement.

 

[powell30]

If he has no positive pressure causing the trap to bubble the smell can't travel past....he confirms access chamber clear so it is unlikely he is generating positive pressure but we could always recomend he gets his drains cctv'ed or he could do as i asked first.......

 

[mcs135]

MCS have you done what i asked you to in the other thread you posted on this subject??......smells can't 'travel' past a water seal. Either the seal is being breached or the water is rancid and your telling us the gully is clean and water sweet...(within reason)......do what i ask and report back....then we can reassess.

The water in the gully is fine. I will check the level after flushing the toilet to see if this is generating a vacuum and sucking the water out of the gulley; but this will be when I get home from work.

 

[powell30]

Two scenarios then.....if the line is partially blocked the water when it fills the whole line will create positive pressure in front and negative pressure behind itself......this will draw the water from the gully in order to suck air......or as softus has suggested it is possible that the water will push back up the line and this positive pressure pushed out your trap ie bubbles.......so check the toilet run plus, check the air inlet for the stack is clear (this allows air into the run toi equalise pressures) if this is blocked or partially blocked it can cause these effects too

 

[mcs135]

I wouldn't mind betting that the stack could be blocked. Can this be rodded from the bottom?

 

[powell30]

If you have access yes. Where does your stack terminate? Can you rod down it if needs be plus check if you have an air admittance valve on top as these can stick (they are one way valves to allow air in but not out) Although i would expect this only if the stack terminates say inside your loft space. Note even partial blockages can cause pressure differentials so althought your toilet flushes it doesn't mean the line isn't degrading and partially blocking

 

[mcs135]

If you have access yes. Where does your stack terminate? Can you rod down it if needs be plus check if you have an air admittance valve on top as these can stick (they are one way valves to allow air in but not out) Although i would expect this only if the stack terminates say inside your loft space. Note even partial blockages can cause pressure differentials so althought your toilet flushes it doesn't mean the line isn't degrading and partially blocking

I will need to assess this when I get home - although I do know that, being a 1920's house, the stack is on the outside above the level of the gutter.

 

[Softus]

If he has no positive pressure causing the trap to bubble the smell can't travel past.

That is not a true statement.

 

[mcs135]

Two scenarios then.....if the line is partially blocked the water when it fills the whole line will create positive pressure in front and negative pressure behind itself......this will draw the water from the gully in order to suck air......or as softus has suggested it is possible that the water will push back up the line and this positive pressure pushed out your trap ie bubbles.......so check the toilet run plus, check the air inlet for the stack is clear (this allows air into the run toi equalise pressures) if this is blocked or partially blocked it can cause these effects too

I have now cleaned the gully, which just has clear water in and I have flushed the toilet. There was no drop in level or bubbles coming through.

Do I still need to check the stack is clear (a job that will require a very tall ladder to access the top)?

Or does this mean the problem lies with the outlet pipes from sink, bath & shower?