depending on the sand it can jam up a pump really well then you have to shut it off which allows some back into the tank. results in a mess.
simply siphon the sand out with a decent-sized hose. your water will remain exactly as it looked before and it will remove the sand entirely.
when adding new sand back in i swish small amounts in a bowl to remove floaties then strain it a net-full at a time under running water to remove fines. it goes back into the tank almost crystal clear.
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