Just reporting back—
Using a 2 inch wide Python siphon with
@Mr.Shenanagins technique and a 100 mesh paint strainer worked well for Aqua Naturals Delta Sand (a coarse sand) and Palmetto Pool Filter Sand (fine sand), but didn’t capture all of the Aqua Naturals Galaxy Sand that made it through the siphon. There was a fine silt that made it through. I’m going to try a 200 mesh next Monday, and I think that’ll fix it.
I also put a thin sponge with large holes inside the siphon to stop any critters getting through. I just needed to put a small filter sock over the opening when I lifted it out of the water, otherwise junk that got caught in the sponge fell back into the tank. I can’t get into all the nooks and crannies with this, but it’s a vast improvement. I’ll just have to keep using the turkey baster on those spots. It felt good to get so much crud out, lol!