I don't get this common meme. Nearly all fuel tanks have the pickup at the lowest point of the fuel tank, where the heavy grot settles. How does low fuel alter this? At low fuel only stuff floating on the fuel surface would get into a pickup, and then only as you run dry.
I'd be looking at the security of the breather where air is sucked into the tank to replace the fuel used. Also not everything that looks like sand is actually natural sand. There's plenty of stuff that can break up into particles when supplied through a dodgy fuel suppliers delivery system.

