I've never used an overflow box before but ive got a DIY PVC
overflow. It's very low profile and ultra quiet, it doesn't disturb us at all in the living room. It's cheap and easy to setup and as long as you setup he overflow and the sump properly you won't have to worry about flooding if either the overflow or return pump fail.
Where most people have issues is that they don't leave enough room in either the DT or Sump to hold extra water should something fail. In my setup I have 10gallons of room to work with in the sump. Which may not seem like a lot but there isn't any possibility that my overflow would allow more water to drain if the return stopped working.
Edit: and to add another detail which was mentioned above. Your return line placement and fail safes are important as well to prevent back siphon. Which is easy enough...I know people use siphon break wholes but I think they are risky. I prefer to place my return (which is all PVC
) just above the waterline with elbows. This way no water can back siphon because it never has the chance. If in the case your overflow stops working and then your return pump fails because it was running dry/low and the return line was submerged due to your return sump section being empty then water will only back siphon so much thanks to the solid placement of the return line. The other great thing about it is that at a certain point where the water gets low the elbow will naturally start sucking air and break a siphon on its own.
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