Hmmmm Ok so it's FW but I think my next reef tank will be like this

[AndyL]

Dead things? plumbers snake or creative use of a mag float...

I've seen a few of these over the years pop up on various boards... Generally they've got some water flow through (bigger powerheads mounted to push/pull water through, you can spy it in a few of the pictures - but you also need a run of plumbing between the tanks (keeps the levels equal in each)

I think the biggest technical challenge has to be initial priming - and regular draining of air - obviously that coffee shop one has been neglected...

I'd imagine one would add another hole to take excess water in case of a dump to a drain... (simple hole drilled at top of tank)