I have a question concerning washing machines. I know that the codes forbid that draining hoses be connected to kitchen traps. I was wondering if the plumbing codes also require that anti-siphon devices be used for the draining hose or if there are any other rules regarding backfilling into the washing machine itself.
The washer needs to drain into a standpipe or laundry sink with an airgap, which is usually provided by the integral bend at the
end of the washer drain hose. That's all the anti-backflow provision it needs. There will be no siphon action unless the end of the hose
is below the water level in the washer, which is not going to happen with a proper standpipe.