As noted before, this is an incorrect line of thinking. I get it that YOUR drains are clear, but that, in no way, means other engines will be. One experience with one engine doesn't mean it's the same for the tens of thousands of others out there and promoting that can only lead to someone following misinformation and ending up with a huge repair bill.Drain hoses are about 5/8" inner diameter in my recollection from pulling a couple off to get at spark plugs in Spring. This is huge compared to a grain of sand. Hoses were completely clean. You can pull them yourself as part of winterization but this fear seems to be totally groundless. Of greater likelihood might be UFOs or Democrats cutting taxes. Just drain the block with the one point system Mercruiser invented to make it easy. Pull the hoses to inspect for clogging every time you replace plugs as you gotta get a couple out of the way anyway.
These lines can, and do, get clogged - I've seen it many, many times. I'm offering guidance based on many years of real life experience... and quite honestly, with a heck of a lot more boats than you are experienced with. I don't mean that in a negative way - just that facts are fact.