Infinite Liquid Source?

I've heard that there's a way to make an infinite water source, so I tried it with Ooze, and it didn't work?

I fear using up all the natural ooze in my area, so is there a way to make an infinite source?

I've tried the 'dig three blocks, then let two flow into each other' trick. The game wouldn't let me fill the bucket in the middle spot.