The hydraulic tank is for your slide-outs, and does not have a connection to the jacks. Earlier, you said that you could not raise it high enough to get it on the hitch. If that's the case, you should crib under the frame, both sides just behind the jacks as close to the height of the frame as possible, then lower it to the cribbing. If the jacks are totally inoperable, you may need to use hydraulic jacks under the frame (again, both sides at the same time) to lift, the position the cribbing. Heavy duty jack stands could also be used if there is enough clearance.
When I replaced my jacks with the Ground Control system, I raised the rig up higher than usual, cribbed with 4x4 pads, then lowered onto them. That way I didn't have the truck in my face while working in the compartment. Fortunately for me, the OEM jacks were still functioning.