drain question

[Stephen]

Hello,

I understand that drain pipes can be connected in one of three ways:

1. to a soak away
2. to a special rain only sewer (what's the proper name for this: surface water sewer?)
3. to the same sewer as everything else.

My question is: does the drain need to have a trap if connected to a soak away or rain sewer? Are these just as smelly as foul sewers?

I ask because the drain pipes on my house, and all the others in the street, go to a 100mm clay pipe with no visible trap and yet they do not appear to be particularly smelly.

How could I find out if they go to a separate sewer or soak away? I know I could pour dye down the drain and see if it passes under the manhole but if it doesn't, that wouldn't tell me where it goes.

I'm just curious why there is no trap or were they not built like this thirty years ago (the house is mid-70s).

Thanks, Stephen.

[Limey Lurker]

We didn't need traps before the terrorist threat began.

[Hugo Nebula]

On Wed, 09 Sep 2009 14:36:58 +0100, a certain chimpanzee, Stephen randomly hit the keyboard and produced:

To a soakaway or water course, no. To a separate sewer, usually not. It is possible that a separate sewer eventually reconnects to the foul drain further down the line, so either the connection between the two sewers should be trapped, or each inlet trapped.

Separate drainage is a relatively modern invention, along with treating the sewage. In order to stop the sewage works overflowing every time it rains, the surface water is sent elsewhere. I would expect an estate built in the 1970s to have separate sewers.

[Stephen]

That must be it then. So surface water sewers do not need traps because they don't carry smelly stuff? I've learned something new.

Do many people realise the sewers are separate? What is to stop someone inadvertently connecting their washing machine to a drain?

[Roger Mills]

Very little! We have separate foul and surface water sewers - but soapy water comes down our surface water sewer when it hasn't rained for ages, so

*somebody* appears to have connected their sink or washing machine to it. Fortunately I haven't seen anything *really* smelly coming down!

FWIW, my house's original connections (built about 1968) to the surface water sewer were all trapped - but connections from subsequent extensions haven't been.