Running washing machine waste - long "trap"

[mlippett]

I have some routing issues with my grey waste - I have to get over or under another appliance. I don't want to go up, as the washer will back-fill. I was wondering about the possibility of installing the usual pipe down to floor level (for reasons I won't go into I can run a 40mm pipe along the floor), but rather than having a trap there, installing an elbow and running horizontal along the floor for 2m, then popping up about 30cm before T-ing into an existing waste pipe. AFAICS this effectively creates a 2m long trap. Is that OK?

It's only going to be like this for a couple of months, so a semi-temporary solution is ok.

Thanks in advance for any advice.

-Mark

 

[Radioman]

Won't that be a dead leg of grey water?

 

[mlippett]

Hi Radioman,

I don't think so, since new grey waste from the washer will cause the "long trap" to overflow into the existing waste pipe.

Cheers

 

[Radioman]

But it won't symphony out so you will have water laying

 

[Riley]

Agreed don't think that amount of water will siphon.

 

[rpm]

The pump is not designed to work like that and you will shorten the life span of it, that is if it even can do what you propose. The water will not syphon away so any new water will have to push the old water in the pipe along first.

 

[snowhead]

Use a Hepvalve in the Horizontal;

Hepvo Waterless Valve

 

[rpm]

The 30cm length of pipe rising at the end is the issue here leaving old water in the horizontal section of pipe.

 

[mlippett]

I may be missing something here, but it's like us have taken the bottom of a normal trap and stretched it to 2m, with the 30cm rise being the opposite end of the trap. As with all traps, it'll work under gravity, not syphoning - once it is full, adding water at the machine end will cause old water to spill out at the other end.

mark

 

[Frelon]

Mark

That's what I thought! Maybe it is too complicated for some plumbers to understand!! Or am I the dimwit here?