Long waste run, AAVs and the like

[DCC]

I'm putting in a long 40mm waste run say about 3.5m or so to a kitchen sink, this is fine and doesnt cause syphoning (tested). What I want to do is extend the run a further couple of meters to where the dishwasher will be located.

With a standard P trap and the dishwasher outlet pushed into the top pipe there is pretty severe gurgling from the dishwasher trap when a bowl full of water is lobbed down the kitchen sink. Need to fix!

What I'd like to do is use one of the dishwasher attachments that are a small section of 40mm pipe joined to a tapered and ridged nozzle that look a lot more secure than hanging the outlet pipe into a P trap.

If I use an inline trap like a HepVo this will sort out the gurgling but do I need anything upstream of the dishwasher connection to allow air in (it'll be sealed at the dishwasher connection itself)?

 

[muggles]

OK, first things first...I don't think a HepVo will sort your gurgling out. I suspect that the gurgling is caused by the water from your sink pulling the trap in the dishwasher upstand, and pulling air through as well.

When you first tested the kitchen sink waste, was the extension for the dishwasher already in place? Does it gurgle whilst the sink bowl is clearing, or a short time after it's cleared? If it's after it's cleared, get a vented sink trap, McAlpine code is SC10V, plumb centre will understand if you quote that at them. McAlpine call them Silentraps. If it's whilst the bowl is clearing, and if you have space, tee in a 1 1/2" Air Admittance Valve just downstream of your dishwasher upstand, and that will also cure it (you could actually use this second option anyway but often there isn't space). The upstand for the AAV should be as high as possible, preferable taking it right up to almost touching the underside of the kitchen worktop.

Generally hanging the outlet is the way to go, I wouldn't advocate sealing the upstand, particularly as you're having problems anyway. If you're worried about it coming loose, clip it to the wall with 28mm pipe clips.

 

[DCC]

Thanks for the thoughts.

The gurgling is after the sink has emptied as it pulls (or tries to pull) the water out of the P trap for the dishwasher. I'm quite limited for space under the sink so I'm using a space saving trap. However there is lots of room round by the dishwasher. You'd recommend a normal trap + admittance valve just before it? Guess that could work.

I was thinking the HepVo would be a replacement for the dishwasher trap.

 

[Richard C]

I'm putting in a long 40mm waste run say about 3.5m or so to a kitchen sink,

This exceed the Building Regs. limit of 3m for an unvented branch in 40mm.

this is fine and doesnt cause syphoning (tested).

Stroke of luck; but does it still maintain the minimum 75mm depth of water seal required on a sink unit!

What I want to do is extend the run a further couple of meters to where the dishwasher will be located. With a standard P trap and the dishwasher outlet pushed into the top pipe there is pretty severe gurgling from the dishwasher trap when a bowl full of water is lobbed down the kitchen sink. Need to fix!

Ahh that pushed it a little too far!

What I'd like to do is use one of the dishwasher attachments that are a small section of 40mm pipe joined to a tapered and ridged nozzle that look a lot more secure than hanging the outlet pipe into a P trap. If I use an inline trap like a HepVo this will sort out the gurgling but do I need anything upstream of the dishwasher connection to allow air in (it'll be sealed at the dishwasher connection itself)?

Follow Muggles advice; if in doubt consult the Building Regs. or a manufacturer's design guide, that's why they were written.

 

[jay1]

a hep vo is designed to eliminate the need of an aav