How do I drain my washing machine?
Washers are supposed to drain into a vertical standpipe 18-30 inches in height above a trap. The trap arm must then be vented before waste water can be discharged into waste piping. I don't believe there are lesser requirements allowed for greywater discharge. By the time this all is installed, the washer must pump up to within 6 inches of the ceiling. How high the washer can pump is dependent on the model. Once this height is determined, you can calculate how high the machine must be to meet all requirements.