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