The only reason for a “no-knock” warrant is that there is something on the other side of the door worth killing or dying for.
IMHO, “Flushing the evidence” is not a reason.
Otherwise, how do you tell a cop from a criminal?
You don't. You can't.
Anybody breaking down your door at 0h-dark-thirty is a criminal. You dare not assume otherwise. Act accordingly.
Police and Judges: Take note. We the People, your masters, are armed. Be polite and be professional. Show up during the day and announce yourselves. Show a warrant, or go away.