Usually that type of smell is from the water heater because the anode has rotted, which it will do on a regular basis. This tank should be sanitized if not in regular use and after being winterized.
If the fresh tank and lines have not been sanitized for a while...you can add bleach, pour right into your white water hose before you fill with water.(this will sanitize the hose too) You don't need a whole bottle! For a 1/2 tank 1-2 cup of bleach will be enough. You should fill the whole tank or at least 1/2 then drive it to stir it up, then turn on your faucets one at a time to clean all the lines, then drain the tank either into the gray tank or through the drain valve. Then you will need to add fresh water and run through the whole system until it does not smell of bleach. It helps to add white distilled vinegar to do the last flush as it will remove any residual bleach smell.