by oasis » March 11 2010
This is the sort of question that would be easier to answer with a sketch provided, but here goes:
1) is this really a washing machine, or is it a dishwasher? If a dishwasher, the cleaners are typically salt-heavy and not great for plants...
2) if you go down then back up to the height of the water in the machine, at which point a tee goes up to a vacuum breaker and down to the landscape, that would prevent siphoning.
However, you'll have stagnant, fetid water in the U-shaped line. Not a lot, probably acceptable if no alternative, but...
3) your best bet would be to have a vacuum breaker right under the counter top, then go down.
Art