I think of strainers as piles of logs, sticks, branches, etc that have accumulated and are waiting to accumulate a swimmer. As for a seive, that could be rocks that do the same. Its quibbling over fine points from here on out. As Keck said, "They're used interchangeably on the buzz because they esentially mean the same thing - stay the hell away."
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse