Enhancing my overflow rain barrel with a check valve

Recently I put a short barrel under my deck to hold excess water from the barrels under my downspouts.

I put in a float valve to keep it from overflowing.  You can see in the picture below that it is at least 8 inches lower than my other barrels. 

This works.  It's great.  I can fill the overflow barrel from my over barrels.  The problem is getting the water back out.  If I connect the two barrels together using the hose bibs the water from the higher barrel will move to the lower barrel and cause it to overflow.  I have to make sure that the water in the higher barrel is lower than the lower barrel before connecting them.  That's a nuisance. 

There is a solution.  It's called a check valve.  It's a valve that only allows the water to travel in one direction.  The next problem?  Finding a check valve with a low cracking pressure.  That's the amount of pressure needed to open the valve so the water can flow.  All of the check valves sold at Lowes and Home Depot had a cracking pressure of 2 psi.  Using gravity you get 0.433 psi per foot of elevation.  My short barrel is about 3' high.  So when it's full I'd get 1.29 psi.  When it gets low it'd be less. 

Luckily we have the Internet.  I was able to find a low cracking pressure (0.25 psi) check valve at zorotools.  It wasn't cheap.  I paid ~$15 for including shipping.

It was a lot larger than I expected it to be.

I ordered one with female pipe threads on both ends.  I used a 1/2" MPT x 1/2" MPT fitting on the intake side and screwed it into a 1/2" FPT to 3/4" FHT fitting.  This gets attached to the hose bib on the barrel.  On the output side I screwed in the standard 1/2" MPT to barb irrigation fitting.

I ended up swapping out the straight fitting for an elbow.

I rotated barrel 90* to make it easier to tie back into the drip lines already under the deck.

All of my rain barrels are plumbed together. The irrigation tubing connecting them intersects under my deck.

In short, when my rain barrels get higher than the overflow barrel they will fill it until it's full and the float valve closes.  As I drain the barrels the overflow barrel will drain as well.  This gives the whole system more capacity while keeping the overflow barrel of the way and out of site.

I have plenty of room under my deck.  I'm going to see how this works and then probably add a few more barrels under there.