Washing machine on a 30C cycle. Batches of Lego in a lingerie / delicates bag.
Dried in the airing cupboard on a towel and agitated a couple of times a day.
I bought a load off eBay which was disgusting. Included alien plastic building blocks as well as fluff, bits of tissue (clearly used for something), moss, dried insect abdomens, hair, some which appeared to be head hair and some left me hoping that the batch had been played with by a curly headed child. But I suspect that it hadn't. Plus a couple of other unpleasant items - see if you can spot what they are. Centre right in the photo.
This got sorted with the Lego thrown straight into my bath which had a Jeyes fluid solution in it.
After a trip through the washing machine - with a couple of towels in there too for padding - it's come out pretty well.