What drains are there for toilet/sinks?

[nameisme]

Hi all,

Can anyone explain how our drains may work?
I live in a terraced house in the middle, there are 6. Im the 3rd one down.

So we have a manhole about 4 feet away from our back wall under our decking. The water runs ofcourse in one direction only. When our neighbours upstream run their skins or shower water flows though it. However when they flush their toilets nothing comes down it?
So does that mean theres a seperate drain pipe for dirty water and one for clean water? And if so are they connected at some point somewhere as I know when the drains got blocked not long ago the smell from this clean water pipe was horrendous so I presumed there was just the one pipe, one for bith dirty and clean water. Scottish water unblocked the drains from this drain under my decking.

But as I have discovered this evening when my neighbours flush their toilet nothing flows through this drain? Anyone maybe explain how our drain system may work?

Ive added photos to show how the drains etc are. The thick back drain is the toilet drain and the grey ones are for the bathroom sink and kitchen sink/washing machine.

 

[CountryFan]

Neither are clean water, all just classed as foul water. It would be uneconomical for a separate foul and foul drain, but maybe there was an alteration at some point? Drains are usually: Separate Foul and Separate surface or combined/partial combined.

 

[Diver Fred]

Which way does the water flow in relation to your pictures?

 

[robinbanks]

However when they flush their toilets nothing comes down it?
So does that mean theres a seperate drain pipe for dirty water and one for clean water?

Perhaps. How long did you wait? It can take a very long time for manhole X to show a flush at Y

 

[blup]

Using a colour dye might help identify the source. What goes in as “clean” water can appear foul as it passes through the underground pipes. Older properties were built with “grey” water entering the foul drainage system

 

[Hugh Jaleak]

It may look 'clean' but Sinks, Showers etc, are classed as 'Grey Water' and must go to the Foul or Combined (as in foul and rain water in the same pipe), sewer. It may look 'clean' but is not of a quality where it can be discharged directly into the environment.

I would check under your decking that there isn't a broken pipe and the Neighbours waste is spilling out over the floor somewhere, if all looks OK, then I wouldn't worry about it too much, Upstream will soon realise if there is an issue, and their Toilet backs up. Very unlikely to be two pipes.

 

[nameisme]

Which way does the water flow in relation to your pictures?

Thanks. If you see the photo of the deckchairs the water flows from right to left.

Both neighbours upstreams toilets do not flows into my manhole at all. Only their sinks, showers and baths do.

 

[ChrisJP]

When you flush YOUR toilet do you see anything going through your manhole?
If you don't, I suspect that the toilet drains from all the terraced houses combine and this single pipe is teed into the pipe that runs through your manhole someplace a bit downstream of it. That would explain why you still get bad odours in your manhole

 

[nameisme]

Well our toilet is down stream from the manhole in our garden.
I spoke to a drain specialist in my area and he said its common for there to be a grey water drain and a foul water drain. He said the foul water drain is a 4" but the foul water is 6".
The black pipe in the photos is the toilet pipe and the pipe for the sinks etc are the grey pipes. The black pipe is bigger but that doesnt nessecirily mean the grey water and foul water drains are different sizes does it?