What to do with Effloresence

We have a water tank in the foundations of the garage. It is made from concrete block filled with concrete. and the parts that are out of the ground due to the slope of the property, are rendered and painted. Problem is after nearly 15 years internal moisture has found its way through - lifting paint and in places the render - also large areas of effloresence. What can I do to repair the damage and repaint considering the surface is damp.

http://img.photobucket.com/albums/v6...ept2009021.jpg

http://img.photobucket.com/albums/v6...ept2009022.jpg


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