Jim; I used about 3/4 of a gallon thats all I have left. As long as the parts stay covered it works. I think agitation helps.I just bought a pump from Harbor Freight for $10, I'll try that. If you let the parts sit in the solution extra time after its ready it has a carbon looking stuff on the metal, but all I did was move the bucket so the solution swished around and it removes it. The good thing is no matter how long you leave it it doesn't hurt the parts. When I first got it about 3 years ago when I was in and out of the hospital I put some in an open container and forgot about it for a few months and it evaporated. I rinsed off the part that was in it and was good to go. From what I know you can keep using it. Eventually it will get filthy and it will need replacing but not for a long time. If you let it settle and siphon off the junk in the bottom it will help. I think You can add a little water if it evaporates but not too sure it should say on the web site. I always degrease the parts to help keep it clean.
This is where I got it check out the videos of it working.
http://www.ultraone.com/
Here's the gas pedal linkage.