When I was do my pwc
's on my small tanks I use a premarked painters bucket from a home improvement store. It has the gallons listed right on the side so you can take out exacly what you want and know exactly how much to put back in. I go by 3g pwc
's since I can't lift the bucket with more than that! LOL
Glad some of my posts have been helpful.
I do tend to ask some basic silly questions so it should enlighten those who dont' wanna ask.
Good Luck! keep us updated with what you end up doing!