Yes, the washing machine.
Thanks to the internet, I learned that this was the most effective and painless way of cleaning a large amount of Lego at once. Just chuck the separated pieces into a laundry bag (usually used for bras etc.), add a little detergent, and set the machine on a delicate or hand-wash cycle.
The results are surprisingly good; just be careful of putting in large and/or transparent pieces because they might get a bit scratched.
Once of the most interesting things about putting a lot of separated Lego into the wash is the amazing way that some of the pieces connect – surprisingly firmly – all by themselves in the rough-and-tumble.
The picture above is from my latest batch. That plate in the middle of the photo somehow had 7 different pieces firmly lodged on it, and all but one neatly lined up next to each other.
Turns out I'm not the only one who has noticed this phenomenon, and some have even done it for science.