Question About Overflow/Sump Set-up

giankr

Feeder Fish
Jun 8, 2022
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I recently bought a 125 acrylic aquarium with a sump off facebook marketplace. The overflow has 4 holes. I figured 2 of them are returns and one is input to the tank from the sump. There is a 4th hole which is puzzling me. Looks like another return? But it has only a notch in the pvc. I don't know its purpose. Does anyone have experience with this? This is my first sump system.

Thank you in advance!PXL_20220608_202331823.jpg
 

ragin_cajun

Silver Tier VIP
MFK Member
Sep 8, 2013
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South Louisiana
Not real sure, but I’m gonna guess …. The notch cut in the return line is to stop the display tank from siphoning back into the sump if the pumps go down in electrical outage.

I have 2 holes drilled in my return lines for that. If not, my display would siphon real slow into my sump until water level dropped below the output nozzle. That’d be more water than the sump can hold.

So, tbe holes in the return line let air and break the siphon.

I think the notch cut in your 4th pipe serve the same purpose?
 
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