I noticed in the manual that there are list control dampers on the No. 2 and No. 6 MBTs. So, my guess is that the vents for either the 6a and 6c tanks or both may have gotten stuck and need to be opened. There are emergency vent valves that can be operated for each No. 2 and No. 6 tank.
Here's what the manual reads:
"The list control dampers are located at the Y-valve outlet connections on the 10-pound blow manifold. Both list dampers are attached to a shaft that runs through the manifold chamber. The shaft is operated by a hand lever at the after end of the manifold. The handle assembly consists of a push rod at the top of the handle, a handle, a spring, a latch, a name plate, and a bracket. A connecting rod attached to the handle is equipped with a turnbuckle secured with a bolt and nut. Pressing down the pushrod releases the spring, lifting the latch, and leaving the lever free to move inboard or outboard. As the shaft turns, the list dampers are swung to shut one port, or open both ports of the Y. The movement of the lever and the attached connecting rod turns the shaft by means of an offset arm. Outboard movement of the lever causes the damper to restrict the flow of air to the starboard side. Inboard movement of the lever causes the damper to restrict the flow of air to the port side. Normal position of the damper is neutral, allowing equal flow to both sides.
List control dampers control the flow of air to main ballast tanks 2B and 2D, 6B and 6D on the port side, and to main ballast tanks 2A and 2C, 6A and 6C on the starboard side."
Here's the process for specifically correcting Tanks 6a and 6c:
1. Open the emergency vent valve MBT No. 6A in the forward engine room on the starboard side.
2. Open the emergency vent valve MBT No. 6C in the forward engine room on the starboard side.
3. Open the supply flapper valve on the 10-pound MBT blow manifold.
4. Start the low-pressure blower.
5. Open the No. 6A-6C MBT 10-pound blow valve.
6. Shift the list control lever on the 10-pound blow manifold to starboard position to correct a port list.
7. Shift the list control lever to neutral position when the list is corrected.
8. Shut the MBT 10-pound blow valves upon completion of blowing.
9. Stop the low-pressure blower.
10. Shut the supply flapper valve on the 10-pound blow manifold.
11. Shut the emergency vent valve MBT No. 6C.
12. Shut the emergency vent valve MBT No. 6A.