In going by the ratio on the Water Wetter bottle (3-4 caps for every quart of water), I split it and add 1.5 caps since I just have 1/2 quart in the system.
The Danger Den Reservoir has both the inlet and outtake on the bottom of the reservoir at the same height. Pic below:
I'm going to flush the whole system, change the flow to the one i mentioned earlier, and only add 1 capful of WW.