I spent weeks trying to find a pressure reducer that would regulate pressure down to the maximum 5psi and couldn't find anything less than about $200. I am not willing to spend that amount of money when I get do a makeshift auto-filling gravity fed system for a tenth of the price.
I don't have any photos with me at work, but I can explain it well. It did take some time exploring the plumbing section at Home Depot and Lowe's to find out exactly how I wanted to do it, though. Oh, and I used the faucet lines to convert from the PVC connections to the toilet bowl float connector.
I mounted a 2-gallon bucket in the top corner of my coop and ran 3/4" PVC through the bottom down to the base of the coop. I added a male threaded hose connector to the end of the PVC. I connected this to a washing machine hose that has female connectors on both ends, and ultimately to my water spicket. This provides a very clean, leak-free connection to my water supply.
Inside the bucket, I installed a toilet bowl float (new of course) to regulate the height of the water. I have seen them at Goodwill numerous times (new in the box), for a couple of bucks, so keep an eye out. Otherwise, even the cheapest ones at
WalMart work fine. Get just the fill valve. You don't need the flapper or toilet ring, obviously.
For the drain that runs to the watering nipples, you can use the overflow drain for a swamp cooler. They should be very readily available right now, as it's that time of the year, so grab a couple for backup. They are about a doller each. Use a faucet line to make this connection to the PVC as well.
I added a plumbing cap to the very lowest point of the watering lines so that I can clean and flush the entire system as necessary. It really doesn't need it often.
The advantage to this method versus the regulated pressure directly from the line is that I can add electrolytes, ACV or whatever directly in to the water supply. We rarely get freezing temperatures here in my part of Arizona, so that wasn't a concern. Depending on how many chickens you have, you shouldn't need to clean the system very often, either. A bucket lid with a single 1/8" hole will prevent the bucket forming a vacuum, but it will keep all the bugs and dirt out.