hi ylmaya:
You can visit the personal websites of many TRT members ---fairly often there will be some illustration of the plumbing.
It's often not a good idea to have valves on the overflow or upfeed pipe, as cumulative surface growth of sessile organisms can hamper, disable or even pervert the function of the valve. A natural constricition point is a magnet for such growths, and if the pipe becomes clogged, then ...well, you get the idea.
It's usually a case of providing a robust overflow that can handle a lot of throughput, and then selecting an upfeed pump to meet your targets re: circulation.
hth
