You should get the manual for the actuator (the thing that slides back and forth that the cable is attached to) to find out how to reattach the cable. It's probably a "Tie Down" brand and you can get the manual here:
http://www.tiedown.com/aactuator.html
As far as the "little tank" that is the master cylinder that pressurized the fluid to actuate the wheel cylinders or calipers depending on whether you have drum or disc brakes. If you have flakes of rust in the cylinder and fluid, the entire system should be drained, flushed, and bled. If your trailer has been sitting for five years there's a good possibility that you have other brake problems especially if you have drum brakes.
You may be a candidate for a complete new brake system by the time you add up the costs of repairs. I replaced my original brakes with this kit:
http://shop.easternmarine.com/index....2&categoryID=0
Someone will be along shortly to tell you how bad they are and insist that you need stainless steel Kodiak brand brakes but the ones pictured have worked well for me.