This flanged 4 inch Tank Overflow Kit is the Overflow Fitting installed on all Poly-Mart Rain Harvesting Tanks. There is a standard rule of thumb when plumbing your rain harvesting system. Rainwater has to be able to exit your tank (when it's at maximum capacity) just as fast as it can enter the tank. If you do not have an adequate sized overflow, your system could back-up and fail during a large rain storm.
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Monday through Friday, 8am to 5pm (PST)