WM fills with waste water after program finishes

[Benny_the_ball-valve]

A friend of mine has contacted me and describes a problem re her washing machine. After having successfully completed a cycle she switches off the appliance and removes the items from the drum. Sometime later the drum has become partly full of previously discharged water, perhaps containing some of the contents of the trap under the kitchen sink – to which the washing machine is connected.

Any ideas as to what might be causing this problem?

 

[wotan]

I would suspect the waste hose where it couples into the waste fitting is not vented, and therefor creating a syphon.
The usual practice is to have a vertical waste pipe coupled to, but higher than the sink 'U' bend.
The waste tube from the washing machine is hooked into the top of this vertical pipe.
Check to see if it is bunged up with crud! it needs to breathe.

Wotan

 

[Benny_the_ball-valve]

Just taken a look at this and it is pretty much as you describe, wotan.

There is one of those three branch traps under the kitchen sink (where the WM hose is connected to a spigot on a compression ring). The WM branch of the trap is quite caked with old dried washing powder, now cleaned out. The sink seems to drain acceptably but I have noticed that a long section (about 2.5 metres) of wastepipe which is seated on the floor has to rise to join an internal stack. Obviously this was full of discharged water. I will need to repipe the whole section from the trap to the stack and I will put in a standpipe for the WM. What I am bemused by is why there is so much wastewater in the drum of the WM? It seems to have back-siphoned quite a large amount of water that was residing (wrongly) in the watepipe. Anyone seen this sort of thing before?

 

[cmother1]

Yeah - if the lower section of pipe is partially blocked there's a potential for any water being run down the sink to find the easiest way out (ie the spigot for the W/M connection) washing out the trap as it does so. A friend of mine regularly had bits of vegetation in his machine.
You could try hooking up the W/M hose as high as you can under the sink to make it harder for water to flow back through this route.
There's no substitute for a separate waste pipe for a W/M or dishwasher.

 

[Benny_the_ball-valve]

Yes, that seems to describe the situation properly. Thanks, cm1. As Isaid I will repipe incorporating a standpipe for the WM. Cheers.