If you need to connect the containers with flammable substances, such as inside a fuel tank must be washed and cleaned before and before connecting, make sure there are no flammable vapors of the substance residues.
If you need a container with flammable materials inside the tank must be washed and cleaned before. Before connecting, make sure that no flammable vapor residues.
If you need to connect with flammable substances inside the container, such as oil tanks must be clear and clean water. Before welding, and ensure that there are no residual flammable vapors.