In my case, I knew we wanted a 2 barrel design, the same plan can be followed for a single barrel design. Modifications will be noted throughout the instructable.
Step 1: Out Flow Parts List
2 2" DWV MIP Adapter - $0.90 each
2 2" DWV Street Elbow 90 degree Spigot x Hub - $2.01 each
1 2" PVC Pipe (2' section pre-cut) - $2.21
2 2" PVC Tee - $2.49 each
2 2" x 1-1/2" PVC Drain Waste Vent Flush Bushing - $0.86 each
2 1-1/2" x 3/4" PVC Schedule 40 Bushing Spigot x FIPT - $1.27 each
2 3/4" Short Galvanized Nipple - $0.98 each
** I chose not to use this but instead got the PVC schedule 80 (gray) equivalent from my local Ace Hardware for $0.79 to prevent as much metal in the design as possible.
2 3/4" PVC Ball Valve - $2.94 each
2 3/4" MPT x 3/4" MHT adapter - $3.53 each
** While my local Ace Hardware did have this piece in plastic for less, I chose to go with brass here to better withstand contact with the metal threads on my hoses.
1 can of PVC primer and cement - $6.96
For a single barrel design you do not need the Tees or the PVC pipe. You have the option to change the 90 degree Street Elbow with the 45 degree Street Elbow to reduce the bend of an attached hose.
Step 2: Building the Valve Assembly
1. Screw the 3/4" MPT x MHT (Male Pipe Thread to Male Hose Thread) adapter into one end of the threaded valve.
2. Screw the 3/4" nipple into the other end of the threaded valve. Screw the other end of the nipple into the 3/4" PVC Schedule 40 Bushing Spigot x FIPT (Female Internal Pipe Thread).
3. Insert the assembled parts into the Drain Waste Vent Flush Bushing (2" to 1-1/2" reducer) and then into the 2" Tee.
About sealing the joints:
I found that friction was all that was necessary for the valve assembly. You can also use plumbing tape or PVC cement for the non-threaded joints.
For the single barrel design, you will not use a Tee in the assembly.
I chose to use this design over other designs I found online because of the volume of throughput. Other designs using different spigots or hose bibs would reduce the volume of the water coming out of the barrels as well as the gravity fed pressure. With this design I am able to have 2 hoses connected both receiving almost the full 3/4" diameter of volume through to the hose threads (see the final picture of the volume through the valve assembly). The bottleneck in this system is not the valve or piping, but the 5/8" hose or attachment at the end of the hose.
Also, have younger kids who love to help in the garden, the plastic valve offered the ease of use I wanted for them to be able to fill their watering cans or water guns.
Step 3: Connecting the valve assemblies to the barrels
2. Cut the 2" PVC pipe (standard hacksaw will do), cutting two small sections for connecting the Tees to the Street Elbows and a larger section for between the two Tees.
3. Insert the pieces between the elbows and tees to make one complete unit.
About sealing the joints:
Using friction or plumbers tape in the joints will allow you to customize the angle of the valve assemblies. If you find that it is leaking, you can cement the joints later. I found this to be beneficial as we could adjust the angle of the spigot assembly to account for filling water cans, water guns, or other items.
4. Remove the two pipe thread bung plugs from the barrels. These are the plugs that do not have the internal threads in the center of the plug.
(I removed the gaskets from the plugs and put them onto the 2" DWV MIP Adapters but this proved unnecessary as the PVC adapters did not screw all the way down into the barrel anyway.)
5. Screw the 2" DWV MIP Adapters into the bung holes of the barrels until tight.
6. Insert the street elbows into the adapters.
With this, the outflow system is complete.
For the single barrel design, insert the vavle assembly into the 60 degree Street Elbow. Insert the elbow into the 2" DWV MIP Adapter.
Step 4: Connecting the barrels to the downspout
If you choose to use a downspout diverter, there are a number of models available on the internet which connect in different ways. While purchasing one will add approximately $30 to the cost of your project, it will also allow you to use your existing downspout system for handling the rainwater when the barrels are full. See http://www.rain-barrel.com/how_it_works.html for a video explanation of how they work in general.
The most common way for filling the barrels is to cut a hole at the top and install a screen over it to keep out debris and mosquitos. As stated above you must also plan for run-off once the barrel is full. As I already had the spare downspout diverter, it allowed me be create a completely contained system. The only holes drilled into the barrels are a series of 5/32" (smallest drillbit I had with me) holes in the top of the barrels to balance the air pressure in the barrels as they fill and empty.
These are the parts I used for connecting the barrels to the downspout, all from my local Ace Hardware:
1 3/4" MIP to 5/8" barb adapter
4' of 5/8" ID (internal diameter) clear tubing
**This hose fit into the opening of the downspout diverter and also allowed for a larger volume of water to enter the barrels at one time.
1. I used a 3/4" spade bit to drill out the bottom of the one of the internal threaded bung plugs, being careful not to damage the threads.
2. I screwed the bung plug back into the barrel so as to use my homemade wrench to ensure it was tight.
3. I screwed the 3/4" MIP to 5/8" barb adapter into the threads of the bung plug.
4. I attached the tubing to the barb and secured it with a clamp.
5. I followed the instructions with diverter to install it into the downspout and then connected the clear tubing to it.
Step 5: Setting it all up and enjoying free water
2. Position the barrels on the blocks so that they are well supported. I have not found any need to secure them to the back wall of my garage.
With it all in place, I waited for it to rain. A few days later, we received a .21" rainfall. I harvested about 55 gallons from that event. Filling the watering can has never been so fun.