Matching overflows to pump questions

http://gmacreef.com/herbie-overflow-reef-tank-plumbing-method-basics/

With the herbie style overflow, you open/close the gate valve to get the exact rate of drainage to equal the rate of pumpage...like my diction? Herbie overflow is also very quiet. As for the pump size/overflow size, that's kinda tricky. You say "flow rate for 1.5 pvc - 1350 gph". Is that turbulent flow, or laminar flow. Laminar flow is what you'll have through that pipe with a Herbie. Laminar flow is much more efficient than turbulent flow. With a Herbie, you want the backup drain, which will experience turbulent flow at least for a while in the case of stoppage of the primary drain, to be able to handle the output of the pump in case the main, gated valve clogs.

So, you have two drains in your tank, one of them can handle the full flow of your pump, do a Herbie....

I think that pump is way too small. Once you factor in head loss, loss of flow from T's on the return, it won't be enough.

That drain looks like it will work. My only concern is that it will only skim the surface.

Ive drilled tanks and put the bulkheads in the center of the back glass with a standpipe. If I had to do it all over again, I would put the bulkhead in the center and place my "stand pipe" outside the glass. Not sure what the flowrates would be but I would oversize the pumbing outside the tank. This way it would draw water lower in the water column.

Heres a crude sketch


As for the pump, when in doubt go bigger, you can always tee off thr return and loop some of the flow back to the sump


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There is no siphon. Theres a vent at the top. (You could make the vent a foot higher than where it turns down if it helps you sleep at night) The pvc determines the water level of the display tank. Whatever height the pipe is, thats how high the water goes before it overflows down. I havent tested this personally so I dont know how audible it is. im going to convert my 40 tall to this design which has a bulkhead dead center in the back of the tank. For the exterior drain pipe om gonna use 2" pvc with my 1.25 bulkhead so it can purge air easily

There's nothing wrong with the design you posted aside from its purely a surface skimmer. I have a tank with a similar set up. It doesn't pick up any debris and the return comes into the tank near the same altitude in the tank. Basically without pkwerheads the tabk is one giant deadzone for flow aside from the top 3" of the water column.

The design I posted overcomes this concern and has mininal plumbing in tank. Another way around this problem is a chambered overflow box like aqueons mega flow design, but like you said you dont want a big box In the tank.

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