Brine shrimp can live in salt water with s.g. ranges lower than our tanks are, as well as s.g. that is high enough that other life forms cannot survive in, thus producing a sterile culture when grown under these conditions.
They don't remain in a tank or a sump, as the sump pump would pump them up to the main tank, probably dead or dying after contact with the impeller, and those placed in the tank would be hunted down by the tank inhabitants immediatley when placed into the tank.
While adult brine shrimp can be grown from cysts, in the US, it is easy to buy adults from an LFS
or order them from:
If you don't have access to these adults and wish to do the labour involved in growing them out, go to:
RAISING BRINE SHRIMP
If you just wish to feed the newborn nauplii to your tank it is very simple to hatch the cysts in an inverted pop bottle with the bottom removed, and an airline (without airstone) inserted so that it rests down in the cap which is now the bottom.
You can use a wide range of s.g. but for merely hatching, 1.020 would be fine, and in just 24 hrs, you remove the airline and let everything settle. Hatched cysts go to the top, while unhatched if any, go to the bottom, and the nauplii go towards the strongest light source, enabling them to be siphoned off and leaving the cysts behind.
Do a quick freshwater rinse of the nauplii before feeding them to your tank.