Kitchen waste - compression vs push fit for outside? Which pipe? And do I need an AAV?

[Oxbow16]

Hi all

 

Sorry for the long title but thought best to bung all these general plumbing questions together.

 

I'll be fitting a new kitchen sink soon and am unsure on the following...

 

1. Compression vs Push Fit for outside? I know solvent weld is the preferred and professional choice, but I'd really like to be able to dismantle every so often and clean out the pipes...

 

2. Which pipe for outside? If I'm using push fit then I guess the answer is obvious! but if using compression I've read I can use either type of pipe. Which stands up best to the elements? And do both types need painting (have read various answers on that question)?

 

3. Do I need an AAV valve? I'm totally confused as to when they are/aren't needed. For context, the kitchen sink is not connected to any other wastes. And it is open ended , i.e. the open end of the pipe sits just inside the drain cover grate.   EDIT - I should add.  There is no AAV in the existing set up.  However, in case it matters, I will be going from a sink and a half to a single sink, and I'll be adding a dishwasher where does was none before. 

 

Any help would be much appreciated.

 

Thanks for reading

 

Edited June 5 by Oxbow16

[Nickfromwales]

Use solvent weld and fit a couple of T’s and cleaning eyes for routine ‘cleaning out of gunk’.

 

Push fit is shart, compression bulky and ugly as feck, sorry!

 

As for AAV’s:

You only need one if the discharging water can occupy suffice pipe area on its way down / out to create a vacuum in its wake. That’s the main culprit for slurping and *gurgling wastes.
 

If this is a ground floor kitchen discharging into a drain outside, it’ll defo not need an AAV.

 

*Gurgling wastes at the kitchen sink are caused by those horrid combination sink traps where the appliance connects via a stubby spur. This means that the water discharges between the sink plug hole and the trap, so you get to hear every last slurp….

 

PLEASE, T off the waste pipe and install a washing machine trap, and connect the appliance(s) via one of those:

 

 

As your pipe exits horizontally to outdoors you have a T instead of a bend, with a cleaning eye:

 

 

This allows you to ‘rod’ into the sink and down to the outdoor drain.

 

”Minted lamb, sir”. 👌

[Oxbow16]

Thanks Nick, that's all very helpful indeed. 

 

I hadn't even thought of the dishwasher slurps and noises that would be heard using a "stubby" pre-trap connection, so I'm pleased you pointed that out.  I'm good with the idea of using a standpipe for the dishwasher, but I'm confused as to how and where the sink waste and standpipe would connect, especially given their different heights.  Are you able to explain please? 

 

Also, what height does the standpipe need to be relative to the appliance and/or sink?  is there a minimum or maximum?  

 

Thanks again

 

 

[Temp]

20 hours ago, Nickfromwales said:

Use solvent weld and fit a couple of T’s and cleaning eyes for routine ‘cleaning out of gunk’.

 

This. 

 

You can get bends with access..

or make a bigger access out of a Tee and screw cap..

 

 and  

 

[Temp]

9 hours ago, Oxbow16 said:

I'm confused as to how and where the sink waste and standpipe would connect, especially given their different heights.  Are you able to explain please? 

 

I'm not @Nickfromwales but..

 

Typically you set the top of the dishwasher stand pipe as high as you can under a worktop allowing room between the under side of the worktop and downpipe to hook the washer hose in the top. Then run a horizontal pipe from the bottom of the stand pipe along the wall to the outside with the appropriate fall.

 

Somewhere along that pipe you insert an upside down T and vertical pipe for the sink. Normally the trap for the sink is close up under the sink.

 

 

[G and J]

With all these clever things coming in the market is there still nothing better than a standpipe for W/M or D/W connection?

[Nickfromwales]

On 07/06/2025 at 06:54, G and J said:

With all these clever things coming in the market is there still nothing better than a standpipe for W/M or D/W connection?

Nope. Open end of the upstand needs to be a minimum of 3/4 of the height of the appliance iirc, but as an ‘upgrade’ you can close off the connection to the upstand by fitting a compression 90° bend and one of these:

 

 

..which will close off the water from the room altogether. 

[G and J]

I like this plan better than just stuffing a waste pipe down a vertical pipe.  Thank you. I wouldn’t have thought of doing that even though I’ve used these things to connect wastes before. 

[Nickfromwales]

4 hours ago, G and J said:

I like this plan better than just stuffing a waste pipe down a vertical pipe.  Thank you. I wouldn’t have thought of doing that even though I’ve used these things to connect wastes before. 

Knowledge is power.....and you are now 2.56% more powerful. Use this wisely.