Sink waste, air lock? Other plumbing options?

[diy_fun_uk]

Need some advice folks. A few years back I fitted one of these double sink waste kits to mum's kitchen sink. It also has the inlet for the washing machine. See pics below (yes I know the shelf partially blocks the view!) For info she's on the 6th floor of a high rise.

Here's the issue. When running water in the main sink, it drains fine. Whether you run the water and let it drain straight away or put the plug in and fill the sink, either way it drains. Same with the second half sink. However, when the washing machine starts to drain (the sinks not being used), it drains okay at first, then you hear a noticeable change to the tone of the water draining. It's at this point you know it's 'blocked' and the water slowly comes up the main and then half sink. Usually not far, maybe 2ish inches or 5cm in new money. Although sometimes it can be higher, and then mum panics.

When the machine stops pumping, the water then drains.

I've been trying to get my head around it. Two questions for you based on the above info:

1. When the machine is draining, given it pumps water out at a fair rate, is it possible some water is maybe finding its way across to the horizontal pipe that serves the half sink, thus causing an air lock of sorts? There's definitely something that changes when the machine is draining, as I say you can hear a change to the tone of the draining water.

2. Would I be better taking the waste kit off and using separate components, including a vertical waste and u bend for the washing machine? i.e. plumbing the machine waste in a more traditional manner? Something like this for the machine plumbed into the rest of the sink waste? I think this might help prevent air getting trapped?

McAlpine Standpipe Appliance Trap White 40mm - Screwfix

Order online at Screwfix.com. Constructed from high temperature polypropylene with compression outlets. Suitable for domestic appliances. Multi-fit compression outlet suits waste pipes to BS EN 1451-1-2000. FREE next day delivery available, free collection in 1 minute.

www.screwfix.com

 

[terryplumb]

Remove the spigot that the appliance drain hose connects to. Inspect the inlet for a partial obstruction that may be diverting the water into the horizontal section.
A seperate standpipe ,as your link, is always preferable in my opinion .

 

[diy_fun_uk]

Remove the spigot that the appliance drain hose connects to. Inspect the inlet for a partial obstruction that may be diverting the water into the horizontal section.
A seperate standpipe ,as your link, is always preferable in my opinion .

There isn't an obstruction as such, however the spigot has a rubber one-way valve thingy in it. I wonder if that's causing the water to divert into the horizontal section? I'll try removing it next time I'm there. If no joy, I'll re-do with a separate pipe.

Cheers

 

[terryplumb]

Worth checking the trap etc ,for partial blocking. Particularly if it all worked fine for years

 

[diy_fun_uk]

Worth checking the trap etc ,for partial blocking. Particularly if it all worked fine for years

Cheers. Yeah tbh I've had it all off today, checked for blocks etc. Nothing there. It's done it from new. Weird. Like I say if removing the one way washer doesn't work, I'll re-do the lot which will hopefully resolve the issue