There are a few fixes for this problem. The cold water in the toilet tank and the warm air in the bathroom will cause moisture to collect on the tank and cause pooling of water. Then the water drips onto the floor resulting in a dampness and clamminess in the bathroom.
One fix is the polystyrene insulation kit from the hardware store. You must first empty the tank and dry it completely with a hair dryer or similar. Then you line the toilet tank by glueing the styrene foam on with a waterprof glue. This insulates the cold water from the tank so it's not transferring the coldness of the water to the tank, which results in condensation on the outside of the tank.
Another method is by installing a hot water 'mixer' valve. This may work but the costs of the use of the hotwater might be a bit of a drama. Also be careful not to run too hot a water into the toilet tank because it can crack the tank. There are also kits available that will fit at the base of the tank that will capture the moisture and drain it off.
With any of these fixes the fitting of an exhaust fan to help remove the humidity from the bathroom when showering will help. Also if water is constantly dripping into the bowl then see those sections in the Toilet F.A.Q. for the fix because if there is a constant replacement of water in the tank then the existing water does not have the chance to heat to the natural room temperature. So there will be the cold of the tank against the warmth of the room, creating condensation.For reference see our diagram of a toilet