This business about not connecting FW systems to sanitary plumbing
reminds me of a USPH required and approved arrangment for FW flushing
systems.

It's called an "Air Gap" and is basically just a funnel with a pipe
outlet a few inches above it. The funnel goes to the tank for fresh
flush water. The valve can either be manual or perhaps controlled by a
float in the flush water tank. If something goes wrong with the
sanitary system, the water just backs up and overflows the funnel with
no way to get into the potable water.

--

Roger Long