I use a herbie system on my 6' tank.
Here are my particulars...
Tank has dual corner over flow boxes, both double drilled. Left side, I use one hole for my return pipe. Right side has my emergency drain.
Both sides submersed drains are plumbed exactly the same, same fittings, same length of pipes, everything. Under water they both have a 6" threaded pipe that connects to a threaded 1" tee. The tee has one 1" strainer horizontally, one 1" strainer vertically pointing up, the bottom is threaded into that 6" pipe.
Underneath the tank, all pipe is measured so that my true gate valve meets exactly in the middle. I did this so that the force of gravity from each side would be the same.
Height was a problem with my setup. My gate valve is actually lower than the top of my sump which sits on the floor of the adjacent closet. This means the draining water must travel up about 5" of height before draining into my sump. Both the emergency drain and the gate valve line are on seperate drain lines into the sump. Because of the height, I have to ensure my emergency drain always has a trickle of water moving through it, otherwise the water sitting in the dip would go stale and bad.
Because I am already slightly taxing my emergency drain, I use a fairly weak return pump. I have fully closed the gate valve to test the capacity of the emergency drain, which it handled.
I should add I use an ATO, but my sump system is 90 gallons total, when the ATO shuts off, the sensor is NOT fully submersed under water.
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