Plenty of us have rain barrels but we all know they aren't that great for getting the water out when they're near ground level.
I got the idea for this from my water storage kegs.

With this setup, when you go to use the water, you shut off the overflow valve and all others except your watering hose and hook your portable car air compressor to the air fitting and pressurize the barrel for more pressure or to pump the water to a higher level.
The air fitting is a replacement valve for a car tire, just make the right size hole in a plastic pipe cap and shove it in.

The key is the overflow pipe (or vent pipe till the water gets to the top) that is like a drop tube in a Cornelius or soda keg. I took a 3/4 copper to threaded fitting and ground off the shoulder so the copper pipe slides all the way through. Slide it through till it almost touches the bottom (or top) of the barrel.

Haven't actually tried it yet (beyond testing for air tight) but I know how well my water storage kegs work. I'm curious how high I can get the water to flow.

The next thing I want to try is to see how much pressure an empty black barrel will make when heated by the sun.......... might be able to figure out some kind of automatic watering system.