There is no possible way that water could ever be sucked back through the tub fill inlet (being that it is topmost on the tub)...unless the machine was on it's side while in operation, which is not optimal as per the user's manual. The model I fixed was outfitted with a worm-screw type hose clamp between the inflow hose and the "Aerator Assembly" that quite nicely facilitated by-passing the faulty unit with no modification or extraneous parts necessary. I would even argue that I eliminated TWO potential leak points!-NeoTeric
This is an anti siphon device. As was posted the tub would have to overfill and the city's water pressure would have to drop to zero or minus at the same time.
You would have better odds at being struck by lightning while driving, having the President's motorcade swerve into your lane because the lead driver was blinded by the lightning flash, and crash into you while you were scratching off your $100 million winning lottery ticket as you were steering your car in the lightning storm.
Put a barb in the hose and get rid of it.
It is an attempt of another brilliant device mandated by helpful government servants