how close can the holes for through-hulls be on a poly storage tank?

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Washington state
Hello again, a year and some ago i posted here and got lots of advice for my diy storage tank project. Thank you so much! I put in my 1200 gal storage tank, with a submersable pump, and a cycle-stop setup, and it works perfectly! I am so happy with it! All your advice got me through with minimal mistakes. But, i did make one that i am trying to fix. I put the inlet and outlet pipes in through the top hatch on the tank, and modified a garbage can lid for a cover. But the cover fits loosly, and i am getting the occasional ambitious slug / snail invading my drinking water! I have found a tank lid setup , with a screw on lid that will seal much better, but i need to move the inlet and outlet. That means two new holes in my tank, and right now the inlet and outlet are right next to one another. I am concerned about compromising the structure of the tank if i make the new holes and bulkhead fittings too close to one another. Like how you don't drill wiring holes in studs too close, or near the edge. The tank is black poly, about 1/4 inch (maybe a little more) thick, and 48" tall and 8ft diameter. The holes will be about 2" for the outlet bulkhead and 1.25" for the inlet bulkhead. Can anyone advise me on how far apart the holes need to be?


Cary Austin
Staff member
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Lubbock, Texas
I would leave a little more room (meat) between the tank adapters. A thin piece of tank wall between the holes will be a weak point. I would say at least 6", but more would be better.
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