Step 1: Acquire the barrels
I shopped Craigslist and got lucky - found a guy that lived close to me who liberated them from his workplace - $15 each. One had peaches the other apricots - my yard has a new aroma.
Step 2: Barrel Orientation
Since these were "closed lid" barrels I decided to go with an upside down setup for several reasons.
My thinking was that I just didn't trust the thickness of the sidewall for a tap in connection since I wouldn't be able to thread a nut on the backside, so I went with a connection into the bung plug, thus needed an upside down orientation.
This provides for the barrel to be completely emptied, unlike most with a side spiggot - but also required me to build the base platform to elevate them slightly for the plumbing.
Since they store on a second story I had no issues of elevation to accommodate a watering can either so the base was fairly routine to build as opposed to one 2' tall.
Step 3: Platform/Base
The barrels measure 23" around so a precut 2' X 4' of pressure treated 3/4" plywood was used as the base with 8 2-1/2" 4 X 4's scattered around underneath as feet. I Painted with deck paint for extended durability.
Step 4: Downspout Gutter Connection
I removed about 5' of the existing downspout and reconfigured the angle with a new piece to aim it toward the barrel instead. I then used a piece of flex-gutter for the final connection to the barrel.
Step 5: Barrel Input Connection
The cotter pins, wire, & wire tie hold the flex tube into the mouth of the filter - in case a heavy ran might try and disloge it from the filter due to back-pressure.
Step 6: Intake Filter
The filter is compised of a gutter-to-PVC 4" converter into the green 4" diffuser which is actually upside down in this application so I am using it as a strainer instead for form. Inside the strainer goes the pipe sock designed to strain sediment from corrugated pipe used in tile applications. I cut about a 12" length of sock, and tied a knot in one end and rubber banded it around the outside of the converter. My gutters are screened so not much gets in other than smaller particulate.
Step 7: Intake Filter Install
A 4-1/2" hole saw and a little pneumatic grinding opened up a hole for a nice snug fit around the PVC adapter and the squared corners keep it from falling into the barrel. The green strainer keeps the weight of the water and debris from pulling the sock down and away.
Step 8: Manifold System
The 3/4" PVC piping pulls double duty - 1) it transfers water between barrels (as the left one fills the right one seeks the same level) (Assuming both valves open) 2) It delivers the water from both barrels to the hose for watering. The Union allows for easy winter tear down - otherwise you would need to move both barrels together which would weaken the manifold fittings.
Connections: The 3/4" PVC runs into a threaded fitting then into the bung plug (Pre-threaded) but you will have to drill through the bung with a 7/8" spade bit, careful not to damage the threads. I used teflon tape & pipe dope on these 2 connections (Bung plug / Barrel & the 3/4" threaded fitting / bung plug - (DO NOT EPOXY) You will need some rotation play in the pipe once you tighten the bung plug you will need to orient the pipe out to the front of the barrels. If you epoxied the connection between the fitting & bung it is unlikely your pipe will be in the exact position needed.
The dual ball valves allow some selectivity if you want to isolate water in one barrel or another - but for the most part they remain open to work as a unified system.
Lastly the brass male hose adapter at the end of the pipe, connects the hose and runs down to a an inline shut off at the end. This allows the user to access the water anytime without having to go upstairs to turn anything on.
Step 9: Venting
Again double duty - The vent pushes air out when filling (the second (right) barrel) & lets air in for a better head when draining. In order to get the max flow (head) you need a vent on the barrels. The first barrel vents back through the gutter input but the second one had no opening in this setup.
I modified a 2" threaded PVC adapter and a double layer of vinyl screen.
Cut 2 4X4" square pieces of screen then crisscross the pattern. Then lightly grind down a piece of 2" pipe about 3/4" from the end (width of the grinding wheel) then cut off that 3/4" piece at the end to become the hollow plug which holds the screen into place - Cut off the excess screen with a razor knife, and thread it into a 2-1/2" hole cut into the top of the barrel.
Step 10: Overflow Components
There is a few second delay on the barrel equalization so you need to place the overflow on the first fill barrel (left) not the second or you will have water spewing from the top of the filter in a heavy downpour that overloads the capacity.
I used a 1" spade bit for the hole - then used a 1" hose barb / 3/4" threaded adapter to make the barrel connection. I also threaded the PVC elbow on inside the barrel to act as a nut.
Step 11: Overflow
In the case of a heavy rain you have to plan for a situation that you fill the barrels to capacity.
Note the 1" overflow hose which should be able to handle the capacity as it runs into the remaining downspout that used to handle this gutter that now feeds the system.