I have done some continuous flow systems but I prefer individual tanks with an automatic water change system instead,  That limits the scope of any possible problem.  Diseases, filter crash, etc can cause quite a lot of damage in a centralized system.

The one place I did use a continuous flow/centralized system the most was with small fry tanks.  I made fry tanks out of disposable "Tupperware" containers.  These were kept in a plastic tray on a shelf - the tray had a drain line down to an aquarium below which had a filter, heater, and pump.  I also had a system where the drain fittings were tied together with vinyl tubing.  Either works.   I think you will find drip emitters work the best to get a steady slow flow.  Any valves I used would slowly clog from deposits etc.  Because of heavy feeding, the tubs still needed cleaning every day but the fish had a steady stream of treated water.

Ken