I'm fairly new to turtles. I've only had my RES for 2.5 years now. I've had freshwater fish for 25 years, saltwater for about 15 and reef for about 10 years. So that's why you see me post a lot on the equipment / environment forum and not much in the turtle care sections.
I used 50 lbs of sand in my 75 gallon tank and that was plenty for the turtle. That handy sand stuff was I think the same price as you paid. $7 or $8 for a 50lb bag. So you really didn't spend any extra by going to the pool supply store vs. the big home improvement center.
You don't need to clean it but you should rinse it. Rinsing it will wash out some of the dust and fines that cloud up your water. The optional filter setup will do the rest.