2007 Dodge Ram white milky substance in gas tank

Our truck did not start this morning, we took it to the dealership and they discovered a white milk looking substance in the gas tank. The truck has been having some problems with the gas tank and it is burning gas like crazy. The dealer says it is not their problem but I am convinced it is. They have said there is a problem with the evap system and we have had the truck in the shop atleast 4 times for them to fix it and they haven't. Could the white milky substance have anything to do with the evap system? Or do you have any idea what it is or how it is caused?