In that thing I built 6" above this post. Any seawater, even old tank water.
I collect them but you need some pods from anywhere. You probably stil have some in there or you need to get some sand from some ones tank. Just throw some pellets in there every day , pods will grow as long as you don't keep the tank to sterile.
If it's a yellow clown gobi he won't eat from the feeder. I feed them live worms like I feed all my fish. They will thrive and even spawn on worms, mine spawn at least once a week. With most other foods, they will croak. They will also eat small pieces of clam and sometimes small mysis.