I recently purchased two 300 gallon tanks to supplement my existing two 55 gallon barrels, allowing me to do some more legitimate rainwater harvesting. I've been really intrigued by manifold system designs like this one, but my concern is that it might not work with differently sized containers. Would I need to get the tops or bottoms of the different barrels to the same height to ensure they filled equally? Should I order them in a particular sequence of sizes? Any other considerations I should be making? Many thanks!

  • Volumetric timing. Simply time how long it takes to drain both tanks. If need be adjust diameter of pipe to slow or speed up rate of drainage
    – LazyReader
    Commented Dec 24, 2022 at 5:13

1 Answer 1


If the tanks are all connected at the bottom so water can flow freely between them, they will all automatically fill to the same level above the ground, independent of their size. Note that this means that if you have tanks of different height, it is probably best to align the tops of the tanks, not the bottoms. If the bottoms are aligned, the shortest tank will set the maximum height of the water in any connected taller tanks, e.g. once the short tank overflows it will prevent the other taller tanks from filling any higher unless you shut the connection between the short tank and the tall tanks. If the tops are aligned, the short tank won't start to fill until the water level in the taller tanks reaches the bottom of the short tank.

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