Attaching 2 or more rain barrels to 1 downspout

There are several ways to connect multiple rain barrels to a downspout.  We acquired 2 blue & 1 white recycled soda barrels from our local water shed education program when they offered a course about rain barrels.  2 of the barrels were closed with 2 intact threaded plugs per barrel and 1 barrel had the lid cut off.

Without any other openings or spigots, the barrels could not be used for worthwhile rain water collection because there was no way of getting water in or out easily.

Using some cheap plastic rated spray paint we painted the barrels to better blend in to our unfenced yard.

I found that each lid had 2 threaded plugs.  They screwed into the lid of the barrel (note that one is fine thread and the other is course thread).  I read on the Net that the plugs are threaded for a 3/4 inch connection so I drilled a hole (Someone on the Net stated that you could just screw a 3/4 inch metal pipe down until the end cap popped off) in the course threaded plug to accept a 3/4" coupling and then did the same for the bottom of the open barrel.

pvc cement strategic pieces together when
everything is snugged down so you have less to cement later.

Makeshift bulk head fitting for the bottom of the open barrel. Using 2 round hose washers (not the flat ones) I sandwiched the barrel between the male and female 3/4" couplings and hoped that was enough for the barrel to not leak.

Raise the barrel off the ground so you don't have to crawl in
to secure the coupling

3 barrels plumbed together.  Waiting for rain to perform leak testing.

From the picture you can see that the barrels are not perfectly level.  Once I get some rain water in the barrels I can check if any fittings are leaking and also if the barrels are leaning in such a way as to make them topple over with the weight of water.

I still need to add vents at the top of the 2 closed barrels to allow the water level to equalize.  Since the PVC cannot be separated, any maintenance will require cutting the PVC pipes.

I also still need to add an overflow pipe to the open barrel and seal the top so it's not a mosquito breeding ground.

*Update*
After a steady 3 hours of rain the barrels are over 1/2 full and I'm not seeing any leaking at the fittings.  When the rain stops, I'll cover up the open barrel with some screen material and plumb the overflow tube.

*Update 2*
We got some more rain while we were away on vacation and the barrels are now full.  I did find 2 of the barrels are dripping periodically from either the threaded plug or the PVC fitting.  It's not enough to worry about for now.  1 drip every 3-5 seconds on 2 barrels probably amounts to about 5-10 gallons per week.  Hopefully as the water ages, sedimentation or algae will stop the leak and I can worry about it in the fall/winter.

*Update 3*
The weight of the water has caused my makeshift bulkhead fitting on the bottom of the open barrel to fail.  The drip is more rapid now at 2 per second.