Imax1 said..
^^^^^
I would not do that.
Any sand that gets in , and it will , won't be able to get flushed out .
If you only use Gorilla tape to cover the small gap where the pebble got stuck you should not have a problem flushing out sand from the bottom, same true for using foam or plastic to cover the whole opening on the topside, just flush out from bottom-side with garden hose.
We know without anything covering the gap that a pebble can get stuck in it, seems like sand would have a much more difficult time blocking the movement of the button.