i did something similar to waht FHM described with doing outside..his is a bit better of a way though probably if you have a bigger bucket to use especially.
what i did was:
put a siphon in a bucket in the sink, and into another bucket on the floor. set a scrap sheet over the bucket, dumped in sand and ran water over it constantly, with the siphon running. stirred the sand around with my hands (aggressively). the siphon was going into a 5 gallon bucket. once that bucket filled i emptied it and started again, it probably took like 6 buckets for each bach of sand i did. so it doesn't seem like a very efficient method, also it doesn't get any floating debris..and my forearms were sore for two days. haha it was a hell of a job honestly. helped having two people though
didn't think to do it the way FHM sugget, taht would work best probably. just use a big enough bucket so that the sand doesn't splash out..and to really mix the sand up i would put the hose at the bottom of the bucket, put the sand on top of it, and turn it on full blast, maybe move it around a bit also.
i wouldn't let that water go down your drain, as you found out it quickly will clog a drain.