"mm" wrote in message

I dont' remember why the anti-siphon is thought to be necessary, but
it was a good reason. Or was that the sprinkler system?


Similar idea.

The DW is to prevent water from a clogged sink or disposal from backing up
into the DW.

Sprinkler systems require a backflow preventor that does a similar function
and prevents water coming back through, possibly bringing lawn chemicals,
getting intothe domestic water systems.

Households rarely have backflow preventors, but they are becoming more
commonplace. Industry has been using them for years where they connect from
city water to industrial use.