Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Hold the siphon at an angle just a little bit entering the sand, most of it still above the sand. Go slowly, and pull the angled siphon though the sand. Do not push, that will pile up the sand and close off the mouth of the siphon. Then there is a chance the sand will get sucked up into the siphon.
Another thing that helps: Put the bucket that the siphon is draining into on a chair or something, so there is less fall coming out of the tank. That will slow the water flow, so less chance of inhaling sand.
Another thing: Keep one hand over the outlet tubing of the siphon and pinch or fold it to slow the flow if some sand does get picked up in the main tube.
I also use this trick when I am siphoning a bare bottom tank.