Plumbers – sink waste advice

I apologise for asking before trying to find the answer myself, (I have done a 10 minute google) I’m a bit pressed for time as the guy laying my driveway has got to replace a drain tomorrow morning and I need to replace the existing copper waste pipe that will now be too high (drive is being lowered).

The base of my kitchen sink in the house is 1100mm above the drain and at the moment I have a 600mm vertical drop beneath the P trap, a double 90 bend through the wall (in copper) and then another 500mm drop (400mm long) run at 40 degree slope to the drain. Also got a dishwasher and washing machine connected to the pipework below the sink. Pretty sure the pipework should be run much shallower than this in an ideal world.

Without dismantling the kitchen and flooring to get under the floor with a core drill, the new waste will need to exit beneath the kickboards about 200mm higher than it is currently.

With such a short sideways run outside can I pretty much run the pipe as steep as I want, or even vertically? The 40 degrees works as it is, occasionally we get some glugging when one of the machines is pumping out. I’m wondering if I can do what I want and add an air admittance valve inside to stop any glugging when the suction tries to empty the P trap?

I don’t have many options as I can’t move the waste exit sideways due to dishwasher and internal gas meter, the only adjustment I have is the drain can move about 200mm either side of where it is. Aesthetically a short steeper pipe run outside would be better as its smack in the middle of the house.

Thanks for any advice 🙂

I think I can remove the dishwasher and get access under the floor, this means I can take the waste out directly above the drain with a neat vertical drop outside. I think this would be OK with an air admittance valve at the exit of the P trap?

Can you get the air admittance valve a bit higher (the better)?

yeh I should be able to raise it up beneath the worktop. Committed now, just ordered all the stuff for the morning!

Buy a p trap with built in air admittance valve frpm screw fix, mcalpine do them.
You might need to buy a twin appliance trap and cobble them together
This will stop the outrush of water free the washer causing a vacuum and associated gurgling and potential smell wafting up

Do you really have copper pipe as waste pipe below the sink
Thats a proper bodge and i dount would meet current regs
Someone couldn’t be bothered to buy the correct size core drill and do it properly

It’s large bore copper, probably original to the house which is 60’s, it was quite neat until I took a reciprocating saw to it. I don’t know the imperial size but close to 40mm, there was a compression adaptor to connect the original 40mm waste to it.

I bought a new space saving twin sink P trap anyway as the current setup pretty much took up the whole cupboard, having fitted it I’m not sure why anyone would use the standard P traps if your plug hole is in the centre of the sink.

Used solvent weld fittings so keeping it dry until tomorrow before testing. Air admittance valve extended up beside the sink so I’m hoping it will work without gurgling 🙂