Scot,
That's just what I plan on doing although I'm seriously considering just putting in a PVC floor drain instead of the flanges, and gluing in a 2 inch PVC pipe down to the floor across the floor and then up into a bulkhead fitting into the bottom of 55 gallon drum.(The clarifier) Correct me if I'm wrong but both water levels will stay the same right? Then the 55 gallon drum is filled with deer fence netting as before, and a pump on top of the netting pumps the water to the biofilter in a separate biofilter tank, which is a little higher than the fish tank. This then overflows into the fish tank via a pvc pipe to start the cycle again.
The reason I'm interesting in this is, if the mechanics are right, the circular tank will be self cleaning if I add another pump in the fish tank to cause a circular flow. Most likely that pump would have a dual purpose such as another filter and pump or an ultraviolet light and pump.
Of course there will be a drain on the bottom of the califier also to drain the clarifier when the netting is cleaned and there is a water change. Also a shut off valve in the PVC to the clarifier to cut off flow when the clarifier is drained.
Thoughts from Mr. Engineer?
Thats the way I would do it. Bottom tank drain to the bottom of the clarifier with a ball valve. I would also put in a tee at the bottom of the tank with a drain hose attached. I have 2" pvc shower drains. I like these because you can easily take the plumbing apart without having to install unions. They were only about 6 bucks at Menards. They fit through a 3-1/8" diameter hole and come with gaskets.
On the outflow of your biofilter, you could plumb some pvc to create your circular current. You may have to diffuse the flow of water back to your tank to get the right current speed.
If you need more solids filtration then you could side stream with another pump. I would rather put in another barrel with a bag filter for that. Up flow out of your clarifier and down flow into the bag filter. You then put the pump in this barrel. You could still also side stream if you really need it.
You could then run an inline uv system directly out of the pump. With the polished water, you will have fewer cleanings of the uv unit, and it will work better.
What specific goals would you want to achieve with UV? The pond units you see are generally for destroying algae, and may not destroy viruses etc...
Here is an interesting pdf from Aquafine:
Aquafine UV
