Leaving it full of fuel reduces the airspace in the tank helping minimize the absorption of water. Leaving the tank empty increases the airspace and the chances of condensation to build up in the tank. So unless you drain that before you fill the tank back up.... you'll still have water in the fuel. I assume your using ethanol fuel. Even with a stabilizer it will separate... also the ethanol itself is a very strong solvent that will attack your fuel lines, fuel pump diaphragms etc. The best solution is to run non ethanol fuel if you can find it locally. go to Pure-gas.org to find a source near you.