I keep the oil tank on the basement shelf. I stuff some household paper into the opening, as it is usually still slightly wet with oil after the tank is removed and should not collect dust. Works wonderfully. The tank is not really airtight. Otherwise it would "collapse" after the oil has cooled down completely due to the negative pressure.

Upright by no means. The container is not hermetically sealed at all. Especially not at the top connection. The whole lid is removable for better cleaning. Always store carefully and horizontally.
Store like any other oil. Luchtgeschützt, but refrigerator not necessary.

When draining, the oil is then simply filtered and sealed airtight in the deep fryer for as long as it remains there. The container cannot be placed upright because the lid is loose. Therefore, always take it out with both hands and pour it back in, holding the lid. I think the system is great!