I put it in a pot or drinking glass (for small amounts) with a lot of water, stir, and let it sit for 10-20 minutes. Then pour off the water slowly. A few of the grains will float, but most will stay down.
But I stopped washing it, and it tastes fine; no bitterness at all. The bulk container I'm getting it out of at a food co-op says it needs to be washed, but maybe it's the prewashed kind?
By the way, you can cook quinoa exactly like rice-a-roni, which opens up the grains faster. In a glass container, microwave 1 cup quinoa with 2 tbl butter (or oil) for a minute, stir to get the melted butter over all the grains, put back in for 1.5 minutes. It may burn at 2 minutes, so don't overdo it. What you are doing is kind of like popcorn -- heating until the grains burst open.
Now add 2 3/4 cup water and half of the rice-a-roni seasoning packet (because you'll need to make the rice with something later). You could throw in all of it, but their seasoning packets come out too salty for my taste anyway. Microwave another 20 minutes -- uncovered (else it will boil over and make a mess).
I guess if you had a big crowd, you could throw in the rice too, and double the recipe (double butter and water). I wouldn't double the time though (maybe 1 more minute?) -- if you burn it, it's ruined!
If you are vegan, watch out for cheese on the ingredient list. I don't see chicken flavoring on any of the boxes I have (just tons of MSG); maybe they are getting veggie-aware?