Drainage for Washing Machine

[replay]

My drain pipe backs up when draining the washing macine. I have inserted a garden hose and run on full pressure with no backup, but as soon as I hook up and drain the washing machine it over flows again. Could it be a problem with the vent stack? Any suggestions?

 

[Softus]

How does the washing m/c outlet connect to your waste?

 

[replay]

it has about a 3 foot drain pipe which attaches to a "U" trap which then connects to a vent pipe that then drops underground to the main drain line for the house

 

[Softus]

it has about a 3 foot drain pipe which attaches to a "U" trap which then connects to a vent pipe that then drops underground to the main drain line for the house

I don't want to appear too pedantic, but it might be worth us agreeing on terminology before going any further...

The outlet from the washing m/c is usually a flexible 'corrugated' hose of about 3/4" diameter.

If you have a trap, and if it's installed correctly, then the hose will rise to a point as high as the lid of the machine, then be formed into a 'U' shape by a plastic former, which then hooks into the top of a standpipe of about 1 1/2" diameter, at the bottom of which is a P trap.

The outlet from the trap will do one of the following:

1. Join up with another 1 1/2" pipe before doing through the wall;
2. Go through the wall on its own and enter a gully;
3. Go through the wall on its own and enter the "soil stack" - a 4" vetical pipe.
4. Not go through the wall at all, but just enter an internal soil pipe.

So, using the above terminology, I surmise that you have scenario number 3. Is this right?

If so, it sounds like you've lifted the flexible hose out of the standpipe and run water down the standpipe to test it. Is this right?

If so, and if you've correctly simulated the volume and rate of water that gets pumped out of the machine, you should encouter the same blockage.

Do you have any toilets that flush into the same 4" soil stack? If so, are they all working correctly?

 

[replay]

Thank you for your time.

Yes your configuration #3 is correct.

Yes I have lifted flexible hose out of the standpipe and run water down the standpipe using a garden hose at full pressure. (It may be slightly less pressure than the washing machine pump).

I have also used a "drain cleaning bladder" on the standpipe.

Water does not back up when using the garden hose alone or with the bladder attached.

I re-inserted the flexible washing m/c drain hose into the standpipe and when draining the washing m/c it starts to back up.

 

[Softus]

I re-inserted the flexible washing m/c drain hose into the standpipe and when draining the washing m/c it starts to back up.

In that case I deduce that the frothy water from the wmc is interacting with a blockage, whereas the clean hosepipe water is managing to get by.

I would remove / dismantle the trap and have a good look at whatever I can get a good look at. If the trap is the slighest bit gummed up I'd just fit a new one. Ditto any waste pipe that you don't like the look of.

 

[replay]

thanks. I'll work on it this next weekend.