May first comment was going to be that play sand can get in the filter and cause problems. In my first tank, I used playsand and a FluVal2 filter. My problem was that sand would get in the filter, and I would then have problems openning the filter fo maintainence. (The fact I had a goldfish that rooted in the sand didn't help).
If you have not added fish, or if you can temporaroly relocate them, you need to wash your sand in a different way. Basically, what you want to do is get rid of all that stuff that can float. The easiest way to do that is to intensionally stir up the sand and get as much of that stuff floating around in the water. Then empty ALL the water out as fast as you can. Basically siphon it with a VERY LARGE diameter hose. Fill the tank and repeat the process. You will likely have to do it at LEAST 3 times, and more likely 8. But once you've done it about 8 times, you should be able to stir the sand up real good and in just a few moments, almost all the sand will settle back down.
The other way I've done it is to wash the sand a little bit at a time in a bucket. But again, agitate it as much as possible and then dump out as much water as fast as you can without loosing TOO much sand. You WILL loose sand, but hey, its play sand. It's cheap enough to bu another bag if you need to.
