Mix manure (not chicken, causes disease) w/ 1/3 water. Lay out in hot weather for 3 days. Put in (doubled) large garbage bags, seal an leave in the sun. Check everyday for movement inside the bag. When it's really active, pour out contents and sift with mesh wire. Another method is to put them into a large rubbmaid tub and slowly pour in water, the maggots will float to the top. You can then place the maggots in bran or sawdust to remove the smell.