SG1 wrote:
my tanks overflowed last night for the first
time since installation. 40% to 120% in a week. It is sad because the ground
at the base of the tanks did not need the water.

That is were you install the "water feature".


What I did with my rainwater tanks was to run a 6" wide, 3' deep trench
past/through the overflow pipe outfall down to the back yard and
backfill with blue metal.

The idea is that the excess water sinks into the trench and runs
horizontally through the blue metal into the root zone of large bushes
and trees.

Alternatvely, since I have two 90mm overflow outlets (to match 2x 90mm
inflow), one feeds the trench and the other runs through 90mm pipe along
the fence to act as a flusher on the waterfalls off the water feature
(well, it looked nice in the back corner).