If you get high quality pool filter sand here are some attributes it should have:
1. Heavy enough to use a gravel vac.
2. No need to wash (it should come this clean - after all, people are using it to filter out fine particles from their pool). If its the nice stuff, when you rinse it, almost nothing should happen.
3. Heavy enough that it doesn't really fly around the tank when you mix it. Everyone should still be cautious and turn their filters off, but seriously, mine settles out immediately.
After having bought lots of sand - I couldn't be happier with the stuff I had (I went BB recently). This stuff was worth it. Most stuff I bought at stores as "pool filter sand" was not worth it.