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Is it granular or flaky? I would think calcium scale would be more like flakes rather than granular like sand. It's possible that a campground had an upset in their water well and dumped quite a bit of sand into your tank. We've seen that at a few places.
Do you get sand out of your other faucets? If so then you might consider dumping/filling your water tank a few times using the bottom tank drain. Then when the tank is cleaned use the highest water pressure you can and open/close each faucet rapidly a bunch of times to try and flush the sand out of each one.