Retrofitting overflow box plumbing questions

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TheWolfman

TheWolfman

Goliath Tigerfish
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Sep 5, 2010
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Ok so Im setting up overflow on a 30 gallon tank and have some questions. The overflow box will be siliconed to the back of the tank. It measures 6”wide x 5” tall. I will be drilling two 3/4 bulkheads for the overflow. What I’m not sure of is if I should set one up with a 90 inside the overflow durso style, and leave the siphon bulk head open? Or can I leave both open. The siphon bulkhead will be as low as I can put it in the overflow. Should the durso be slightly below the overflow teeth or closer to the other bulkhead? Thanks.
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I would have the 90 point down as low in the overflow as possible without causing a problem. I would install a valve to control the siphon. Have it set just slightly less flow then the return.
Then the other 90 should be dry fit so it can be pointed in any direction. Set it to handle the small amount of water that the main siphon doesn’t.
This will insure a very quiet operation.
You may consider making the second bulkhead slightly larger. 1” this would be added precaution in case the full siphon becomes clogged.
 
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BIG-G said:
I would have the 90 point down as low in the overflow as possible without causing a problem. I would install a valve to control the siphon. Have it set just slightly less flow then the return.
Then the other 90 should be dry fit so it can be pointed in any direction. Set it to handle the small amount of water that the main siphon doesn’t.
This will insure a very quiet operation.
You may consider making the second bulkhead slightly larger. 1” this would be added precaution in case the full siphon becomes clogged.
Click to expand...

I understand the syphon needs to be controlled with a ball valve. Are you suggesting I use a durso for the syphon and the secondary drain? I’m not making the bulkheads any larger because the return side is only going to be 1/2” and I’m not going to be putting that much flow through it.
 
More like a herbie style. Your main drain will be a full siphon controlled by valve as you stated. The other drain will be used as an emergency drain in case the main drain becomes clogged.
It’s nearly impossible to match the siphon to the return perfectly.
You will set the full siphon line just slightly less than the return pump.
So the other drain will sit just at the water surface, taking the very small trickle of water that the siphon can’t.
This keeps the full siphon line from sucking air, and if it for some reason slows or clogs the other drain will prevent a flood.
 
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This is the basic but you will have a 90 on the siphon line. I assume you will be coming from the side of the overflow not from underneath
 
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Thanks BIG-G BIG-G for the help I really appreciate it. I’ve been searching for a way to plumb a retro overflow and there’s no info out there for this style overflow. I will be going out the back of the tank and have a T behind the tank with a cap for cleaning. Should I put a bleeder valve on the cap for either of the drains? Do I need a ball valve on the second drain?
 
You will want the siphon to be sealed. No air should be allowed in or it will break the siphon. The other line shouldn’t matter but it needs to be able to handle your return pump should the siphon line become blocked
 
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