Bad smell from outside drain when neighbours use water.

[Orion_28]

Hello, I live in a ground floor flat that has a drain outside the bedroom window. This drain is for rainwater runoff and is also connected to the bathrooms of the two flats above me.
When either of my neighbours uses their bathroom water the drain outside smells really bad. Especially when they use hot water.
When I inspected this before I noticed that the gully was old and cracked. So, I had this replaced with a new gully but the smell persists.
I'm not sure if the smell is being created when the water runs down the pipes before it gets dumped in the gully, or if it is something to do with the gully.

I have attached some photos to show the flow of my neighbours water.

Any advice would be appreciated.

Drain Pictures

• Orion_28
• 20 Feb 2019

 

[bernardgreen]

It looks like the gully and the pipe from the bathrooms go directly to the sewer without any trap ( U bend or similar ) between sewer and gully.

Without a trap between sewer and gully sewer gases will come out of the sewer via the gully.

 

[Orion_28]

There is a trap underneath the flagstones. Sorry, I forgot to mention that.
The upstairs water gets added to the water in the trap.

 

[oldbutnotdead]

There's no sign of a stack pipe in those pics (which gives the smelly gas somewhere to go when a load of water is dumped into the pipework). Is the smell a stagnant water mucky smell or a sewer methane type smell?

 

[Ian H]

It’s a bodge. The new gully is just a new top above an old gully and it looks like the rainwater downpipe runs under the ground and joins between the 2 in a void.

There should be a trapped gully under the downpipe connected directly to a 4” drain.

 

[mattylad]

Can you try chucking a bucket of water into the gully and see what happens?

Maybe you just have really smelly neighbours

 

[Orion_28]

There's no sign of a stack pipe in those pics (which gives the smelly gas somewhere to go when a load of water is dumped into the pipework). Is the smell a stagnant water mucky smell or a sewer methane type smell?

I don't think there is a stack pipe. The downpipe ends midway up the building instead of going up to the roof guttering. The smell is sometimes methane but most of the time it isn't. When I had the trap replaced and there was nothing but an open pipe to the sewer it didn't smell at all, which makes me think the smell is coming from one of the pipes before the water is going into the gully.

 

[Orion_28]

It’s a bodge. The new gully is just a new top above an old gully and it looks like the rainwater downpipe runs under the ground and joins between the 2 in a void.

There should be a trapped gully under the downpipe connected directly to a 4” drain.

Yeah, I think it was bodged when the building was converted into flats in the 80s. I don't know if there is a trapped gully under the downpipe. Not sure how to find out as it's underground.

 

[Orion_28]

Can you try chucking a bucket of water into the gully and see what happens?

Maybe you just have really smelly neighbours

When the new trap and gully was put in we dumped a whole bucket of water into the guttering just above the downpipe. All the water went into the gully and passed through the trap no problem and didn't smell. It was cold water though. I'm going to try with hot water to see if that makes a difference. Or it might be smelly neighbours haha

 

[Ian H]

There’s no new gully there. The square salt glazed (dark brown) is an old gully.

Make sure the water level in that stays the same and doesn’t rise up to the square lip. If it rises up it can overflow to ground from there and stink without coming accross as a blockage.

Yeah, I think it was bodged when the building was converted into flats in the 80s. I don't know if there is a trapped gully under the downpipe. Not sure how to find out as it's underground.

Pretty confident there isn’t, it looks like it’s 68mm rainwater downpipe all the way. That pipe doesn’t have seals on so will probably leak.

 

[Hot&Cold]

Orion_28 just seeing the snapshot of information you offered here,sorry as well mentioned by others its a bodge or a calculated compromise of very low quality.

Its easy to bring up to acceptable standards,your wc soil pipe is on the same wall see first photo.

Orion_28 maybe consider having it sorted out,cost around £1500 ish to correct the basic existing faults,cost is location dependent. Double it for London

 

[Ian H]

Double it for London

Half it for Rochdale

 

[mattylad]

More likely Gravesend Kent.

Triple it