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Washing Machine Waste Water flowing into the Dishwasher

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My dishwasher (on the left) and washing machine (on the right) are positioned next to one another – see pic A

After repeated washing machine cycles over time waste water from the washing machine builds up in the basin of the dishwasher - see pic B. The waste water will overflow onto the floor if I don’t run an empty dishwasher cycle which removes the excess waste water build up. This is how I get rid of the issue currently which is what I want to remedy.

I am uncertain if the issue is due to my current piping, plumbing and or the way the plumber installed my appliances at the time back in 2010 also being the ages of both appliances. Not sure either if my current pipes are blocked causing the issue, although all water flows down the drain quickly in the kitchen sink. Don’t know if internal non-return valves have been fitted or if this could help. Not sure if the angle/positioning of the waste water piping is too high currently at worktop height, facilitating a run back of the water into the dishwasher either?

It’s difficult for me to get behind my appliances & I cannot remove the inbuilt kitchen bench tops so I do not know where dishwasher & washing machine waste water terminate. Attached are some photos of the current set up:

Pic C – the 2 grey ribbed pipes are for waste water I think for each appliance? It seems this waste water is funnelled into a “separate connection” for each appliance leading presumably into the one bigger white coloured pipe with S bend (pic D) in the background of the photo. I suspect this maybe the culprit & was wondering is this set up is correct installed by the plumber at the time?

Pic E - Pic behind the Washing Machine

Pic F - Ribbed grey pipe is likely the waste outlet from dishwasher (with white panelling) base

Pic G – likely Washing Machine water Inlet

Pic H - likely Washing Machine Waste water Outlet (with grey ribbed pipe)

Pic I – likely Water Pipe in connection with blue/white circular end

Pic J – waste connection underneath my kitchen sink if relevant

Pic K – shows distance from kitchen sink to washing machine & dishwasher

Video – attached shows behind the washing machine which is the first appliance you see and in the background is the secondary dishwasher.

Note: In reverse the washing machine never fills with waste water from the dishwasher & my property is a flat within a group other flats build in 1979.

Grateful for any advice and help. Many thanks
 

Attachments

  • Pic A.jpg
    Pic A.jpg
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  • Pic K.jpg
    Pic K.jpg
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  • Pic J.jpg
    Pic J.jpg
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  • Water Pipe in connection with blue:white circular end Pic I.jpg
    Water Pipe in connection with blue:white circular end Pic I.jpg
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  • Washing Machine Waste Outlet (with grey ribbed pipe) Pic H.jpg
    Washing Machine Waste Outlet (with grey ribbed pipe) Pic H.jpg
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  • Washing Machine Inlet Pic G.jpg
    Washing Machine Inlet Pic G.jpg
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  • Ribbed grey pipe is likely waste outlet from dishwasher (with white pannelling) base Pic F.jpg
    Ribbed grey pipe is likely waste outlet from dishwasher (with white pannelling) base Pic F.jpg
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  • Pic behind Washing Machine Pic E.jpg
    Pic behind Washing Machine Pic E.jpg
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  • IMG_20240522_072459 Pic D.jpg
    IMG_20240522_072459 Pic D.jpg
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  • Waste Water Piping of the dishwasher & washing machine Pic C.jpg
    Waste Water Piping of the dishwasher & washing machine Pic C.jpg
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  • Pic B..jpeg
    Pic B..jpeg
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Neither hose connection or route looks good, but unable to confirm with current pics. Ultimately you will need to pull them out and have a proper look to confirm anything. If both hoses connect to the same pipe you will need a different connection such as a double appliance trap. Presumably the sink waste is extended to accommodate all of this, so must be at the top end of maximum run with little or no fall.
 
On the picture behind the machines, the hose on the left runs up to the white plastic waste.
It should run higher and drop down into the waste, just as the hose on the right does.

It's not easy to see exactly the layout of the white waste behind the machines but it looks like there is a Tee on top of the trap with the branch connected to the trap.
One waste appears to be connected to each side of the Tee, if so it's likely that is the waste on the left is getting water directly pushed across from the other waste and due to it being lower the water is getting back into the machine, assuming that waste is the Dishwasher.

Ideally the main waste run should be lower, but you're probably stuck with at that height.

Layout as I suspect, picture 1 below,
If the above is correct then the simplest, but not best alteration would be picture 2 below, turn the Tee around.
Slightly better, picture 3 adding a white plastic waste elbow on the top ot the turned Tee,


Waste layout.png
Waste layout 1.pngWaste layout 2.png
 
Last edited:
Seems as though the installer forgot to fit non-return valves between the waste pipe and the hose.
Thanks very much for your response. Could you kindly share a web link please of the product: non-return valves I need to purchase from say B&Q or any other hardware store. Your help is very Much appreciated.
 
Neither hose connection or route looks good, but unable to confirm with current pics. Ultimately you will need to pull them out and have a proper look to confirm anything. If both hoses connect to the same pipe you will need a different connection such as a double appliance trap. Presumably the sink waste is extended to accommodate all of this, so must be at the top end of maximum run with little or no fall.
Thanks very much for your response. Could you kindly share a web link please of the product: double appliance trap I need to purchase from say B&Q or any other hardware store. Your help is very Much appreciated.
 
On the picture behind the machines, the hose on the left runs up to the white plastic waste.
It should run higher and drop down into the waste, just as the hose on the right does.

It's not easy to see exactly the layout of the white waste behind the machines but it looks like there is a Tee on top of the trap with the branch connected to the trap.
One waste appears to be connected to each side of the Tee, if so it's likely that is the waste on the left is getting water directly pushed across from the other waste and due to it being lower the water is getting back into the machine, assuming that waste is the Dishwasher.

Ideally the main waste run should be lower, but you're probably stuck with at that height.

Layout as I suspect, picture 1 below,
If the above is correct then the simplest, but not best alteration would be picture 2 below, turn the Tee around.
Slightly better, picture 3 adding a white plastic waste elbow on the top ot the turned Tee,


View attachment 94404
View attachment 94405View attachment 94406
Thanks very much for your response. Could you kindly share a web link please of the product: white plastic waste elbow I need to purchase from say B&Q or any other hardware store. Your help is very Much appreciated with all the details and diagram.
 
Thanks very much for your response. Could you kindly share a web link please of the product: double appliance trap I need to purchase from say B&Q or any other hardware store. Your

Thanks very much for your response. Could you kindly share a web link please of the product: double appliance trap I need to purchase from say B&Q or any other hardware store. Your help is very Much appreciated.

Thanks very much for your response. Could you kindly share a web link please of the product: double appliance trap I need to purchase from say B&Q or any other hardware store. Your help is very Much appreciated.
You need a mcalpine V33WM, the site won't let me post a link. Google it, sold virtually everywhere.
 

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