A Single Water Butt At Ground Level
In most cases this is ideal setup having level ground from your diverter to your water butt(s). Keeping your diverter slightly lower than the top of your water butt will mean that excess water will go back into your drainpipe and avoid overflowing your water butt.
As your water butt starts to fill, so will your RAINPOD and the water levels will always be the same. This is because this system relies on Gravity, also know as a gravity fed system.