I'm willing to make some exceptions. There must be a very good reason to allow such raids, and recoving some drugs is not one of them.
If someone flushes down some drugs, then the police offercers can lift the toilet bowl and recover the contraband. If it is too small to recover, then it is too small to use a SWAT team.
I think the main reason for these types of raids on drug operations is that the operators tend to be well-armed, and often paranoid from meth use as well. They're likely to respond to a knock on the door and a "Police! Please open the door!" request with a hail of gunfire through the door.
With modern chemical assaying methods, "flushing" something simply doesn't dispose of the evidence, anyway, so that excuse is 100% pure BS.