Kitchen wastewater drainage advice

[LiamPope]

Hi there,

As part of my renovation, we're relocating the kitchen sink into an existing extension on the rear of the property. It will have a dishwasher next to it. Unfortunately there's no drain out the back there (there is guttering disapearing into the concrete outside, but I guess to a soakaway - though any ideas on how to investigate?).

That leaves me with a 7m-ish run to the nearest external drain. I guess I therefore need an air admittance valve (or two?). My question is where should it be? Here's a crap schematic of the proposed route. DW I guess will be connected to the sink trap as seems to be common practice (unless there's a 'proper' way since this is a new installation rather than adding a dishwasher to an existing install).

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• LiamPope
• 11 May 2009
• 1

Should I have a valve at point A, B, or both, and/or at the kitchen sink trap? Regrettably I have to go under some floor but that can't be avoided. Where I've shown a vertical offset halfway along the long run is where the under-floor part emerges. I could just as easily keep it at the lower level throughout if that's better. Accommodating the required fall is no problem, even under the floor. The existing drain at the end of the run is the traditional square thing that every old house has (normally with half a dozen overflows/wastes pointing at it). Is this what's referred to as a gulley? Or an open hopper, in which case I'm technically screwed according to part H, right, cos I'm not supposed to discharge into an open hopper?

Any advice appreciated! Cheers,

Liam

 

[LiamPope]

Anyone?

Don't have to ask my BCO, do I?

 

[Hugh Jaleak]

If you want to test where your rainwater pipe may go, lift any manhole covers in your garden. Tip a bucket of water into the gutter and see if it emerges into a manhole. If so, best to flush toilet, to check it is a foul sewer, and not a storm drain. (You cant put waste pipes into rainwater drainage!!!!) If it is useable, you could provide a gulley outside to take existing rainwater pipe, and new kitchen waste.

If not, then run as per your plan should be ok. Id change up to 50mm pipe after 3m though, keep it all at lower level to reduce restrictions, and make sure its accessible to get a snake into should it ever block... Personally wouldnt use the AAV if using the bigger pipe, dishwasher connection as you describe is fine, and finally discharge into a hopper (gulley) is fine AFAIK, pipe should discharge below the grid, but above the water level in the gulley. (Replace iron grid with plastic if need be.)

 

[kevplumb]

put an anti syphon trap on the sink d/w and the rest is as above

 

[Richard C]

I doubt it’s an open hopper, more likely a Back Inlet Gully which will still have a water trap into the foul drain; that’s OK & you shouldn’t need to change it for kithen waste water. The anti siphon traps should work but if you want to fit a single air inlet valve, Building Regs. require this to be within 750mm downstream of the trap (assuming the lengths upstream are within regs.) as long as you can access the rest of the run from one end or the other, it should be OK. Increasing to 50mm might be a good idea as long as you can get a clear route all the way to the BIG.

 

[LiamPope]

Phew thanks guys. For a minute there I thought I was gonna have to resort to this...

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• LiamPope
• 12 May 2009
• 2

So keep it at the lower level, use an anti-vac trap, and see if I can go to 50mm and all should be well. I would consider a swept tee or two pointing downstream in the long run. Normally plugged but providing rodding points if needed. Good idea?

Of course this is all unless I find I've already got a proper drain out the back.

Thanks again,

Liam