Looks to me like your #3 is the tank drain, and #4 is the feed to the pump. Just follow the lines, or take a clearer picture over by 3 & 4.
If the pipe connected to #4 goes to the pump (via a T to the anitfreeze pipe) then, yes, that is the tank to pump on/off valve.
So when you're ready to pump antifreeze in the system you want to close #4 (turn it so the long part is perpendicular to the pipe).
Unfortunately my pics aren't that clear here either:
http://www.thorforums.com/forums/f8/...ific-2448.html
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