Making a bbs hatchery from a 2 liter bottle is probably the most common way. Take an old bottle & cap, and cut it so the bottom is about 1/3, the top 2/3. Using the bottom for a base invert the top 2/3 and insert it into the bottom. You now need an air source, a light source, and a way to keep the hatchery at 80 to 82F. Often the light source provides heat as well, if you have a desk lamp and a wooden crate you have all you need.
Don't forget to add epsom salt or baking soda to increase hardness and/or pH. Unless you have hard water with a high pH just salt will give you a poor hatching percentage.
Here's a link to my hatchery;
http/www.fishforums.net/index.php?showtopic=136880&hl=
I do my bbs hatchery once a day, in the evening. Many times work prevents me from hatching every 12 hours with 2 jars. I pull out the air line, and let it settle for about 10 minutes with a light shining on the bottom. I siphon the bbs from the bottom using a turkey baster.
In the evening, I feed them fresh from the hatchery, and put the rest, along with brine water, into an old 1 pint sour cream container with a hole cut in the top. (That sour cream expired in 2002, I was just laughing at it earlier.) The container goes into the fridge, I feed from that in the morning & after work. The excess gets fed to older angels, corys & bristlenose at the end of the day. The container & air line get rinsed, and the container gets filled with fresh water, salt, a couple drops of dechlor, and baking soda. I then add the bbs & give it a good stir.
I guess the cold slows the metabolism of the bbs enough to preserve the yolk sack, but doesn't doesn't kill them. That method has been working for a few years now.
To drain & rinse I have a large cup that I rubberband a paper coffee filter to. I take what I need from the hatchery or refigerated container, let it drain, then rinse with fresh water. I then walk around the fishroom squirting it in tanks with an eyedropper.
Don't waste money on aquarium salt, go to a farm supply store & get livestock salt. 50 pounds is a couple of bucks, and lasts for years. Get a stainless steel nut from the hardware store & attach it to the end of the air line to keep it in the bottom. Giving the bbs a good stir a couple times daily helps as well.