There needs to be something more vital than 'we think they might flush drugs down the toilet' to justify a no-knock raid.
An ounce might be successfully flushed, but not a kilo. The No-Knock is now used more as a psychological ploy to overpower and temporally stun the suspects. The shock of all the noise (breaking door frames, windows, screaming etc.) and confusion will make most people freeze for a few seconds, increasing officer safety. Officer safety now overrides all other considerations.
That's what the garbage disposer in the kitchen is for.
Well the current practice has done a pretty good job of that, according to statistics which show that a gardener is more likely to die on the job than a cop. Of course taking stupid risks are wrong but what ever happened to the old code of chivalry? Nobody ever put a gun to a man's head and forced him into the police force.