So now you have a trashcan on wheels with faucets sticking out of it.
The wheels are useless, except when positioning the barrel. When it's full, no one will be able to move it.
Now, about the Romans.
If you happen to be a homeschooler, this is an excellent chance to do a unit study on the ancient Romans, and their development of water hydraulics. They knew what they were doing, and
you'll be imitating them with your water system.
The key to remember is: water seeks its own level, and will always run to the lowest point.
Place your barrels accordingly.
With multiple barrels, use garden hoses to run between them. Remember, you can buy one hose, and then the female connectors to make shorter lengths to run between the tanks (no need to buy a separate 25' hose for each connection),
If the highest volume collector is at the lowest point, it will just overflow. The water will not back up in the hoses and go into your extra tanks. So, you need to know which end of your garage is lowest, or which side of your house roof has the greatest runoff. Easiest way to do this is just watch the flow during a rainstorm. The ones that gush over should be where your highest tank is place. You can build wooden platforms for it like we did, or you can just buy cinder blocks and stack them under it to lift it higher.
When that tank fills, the water will overflow down into the next lowest tank, and from that one into the next one and so on.
Above is a finished tank. Remember when you tighten the faucet in place to point it in the direction of the incoming or outgoing hose (and leave enough room for your fingers to screw the hose on and off - I've actually had to put quick connectors on a couple of the first tanks we did just because I forgot my fingers have to fit in there).
This tank is at the back corner of our garage. It has an access faucet on the side (also one of our first - put yours up higher - makes filling buckets easier), the middle faucet is the connecting hose to the tank on the front of the garage, and the faucet on the right is the connecting hose to the other tanks on the back end of the garage. It's sitting on a platform of plywood and cinder block.
This is a finished tank - sitting on its little treated wood platform (our driveway is sloped here, so the platform raises the tank, plus gives it a flat surface to sit on, and looks nicer than cinder blocks sitting in front of the house. To the right you can see the previous drain pipe sticking up where all this water use to just run into the street and be wasted.
Another thing we have learned - try to position the barrels in the shade, or at least where they will get no more than half day of sun. This particular barrel gets sun all day from morning to night, and its very hard on the plastic. The barrel gets very hot and flexible (water stays nice and cool - go figure), and we will probably re-position it in the fall, to the side of the garage, in addition to replacing it with a standard water barrel that contains the weight of the water with less stress on the plastic container.
When we start digging the pond out this fall, watch for Part 3 of My Obsession.