Java Jive said

Note: The ASCII art requires a fixed font to display it properly - if
your newsreader makes a mess of it, copy and paste it into Notepad or
equivalent.

Until recently, I had no problems with a washing machine plumbed into
the kitchen waste via a standpipe as follows:
http://tinyurl.co.uk/cee3
... standing in for ...
http://s28.photobucket.com/albums/c2...ction=view&cur
rent=UnderSink-Before.jpg&refPage=&imgAnch=imgAnch2

From bathroom
|
| Main Soil Stack
|
|
|
|
|
|
|
|
|
|
| | | Washing
Machine
| | Sink | | |
| +----+ +-----+ | |
| | | | |
| | +---+ | |
| | | | Standard Sink U-Trap | |
| | | | | | |
| | | | | |
| +---+ | | |
| | | | |
| | | | |
| | | | |
| | | Standard U-Trap | |
----------/ /-------------+--------------------------------/ |
------------------------+ | +--------------------------------/
| | |
| +---+
|
To sewer

When I acquired a small dishwasher, I adapted the waste plumbing as
follows: http://tinyurl.co.uk/33lv
... standing in for ...

http://s28.photobucket.com/albums/c2...ction=view&cur
rent=UnderSink-After.jpg&refPage=&imgAnch=imgAnch1

From bathroom
|
| Main Soil Stack
snip

Any help gratefully received ...

Looks right.
Try cutting down on the washing powder.

--
zaax
Lightning page: http://tinyurl.com/hmpw9