It is a heavy glass vase I got from Old Time Pottery I inverted on some concrete blocks so they could swim in from the bottom. You have to get wet to submerge the vase and turn it up under water so the vacuum created keeps the water inside. Make sure you have a heavy glass container or the weight of the water will shatter it. (court. of Rick Brown's fb page - Riverview Flower Farm Growing Florida Friendly Plants)
The Grommet team discovers the self-cleaning aquarium from NoClean Aquarium. Waste naturally works its way downward. The design has a reservoir at the bottom, so the waste passes through the rocks where it flushes out through the plumbing system.