Step 6: Add More Barrels
I learned that one 55 gallon barrel can fill up in about 10 minutes of heavy rain. The secondary barrel would only partially fill in that time due to the relatively small diameter of the garden hose. Adding two or three or more secondary barrels, each with its own dedicated fill hose from the main barrel, will work much better, saving more water during those times of heavy downpour.
Make your hose-barrel connections the same way for secondary barrels. The second photo shows a cut-away mock-up of the hose-barrel connection. In this case, a quick-release brass connector just happened to work for the inside job. However, the MHT to FPT adapter is better since it has a larger diameter. A different garden hose valve did duty for the outside job.