I just hose mine down with a high pressure washer and try not to hit the distributor too much with the direct spray.
Yeah, if you get the distributor too wet it might not start right up, and you might have to pop the cap and dry it out, but it won't hurt it.
I used to wrap the distributor with a plastic bag, back in the days of breaker points, but that was never too effective. These days, they don't seem to be affected as much by water as they used to be.