I imagine, optimally, an air-admittance valve would be in order.
But what about dishwashers w/o AAV’s?
Is an upward slope from the dishwasher and then a slope downward
toward the garbage disposal (or waste drain) acceptable?
I have seen some that have virtually completely level d/w drain slope,
and previous owners have complained about dirty water being left in the bottom of the dishwasher after a cycle.
I certainly write those up.
But back to ?: Is upward slope from d/w and then downward slope toward waste drain good enough for anti-backflow?