This item has not been tested with air, water only. Not intended use with air.
This valve will work as backflow preventer between toilet bowl and domestic water supply, if you supply line is 1/2". Standard toilet supply lines can be either 3/8" or 1/2" in size.
This item is 5.5 inches long.
This prevents water from going back into the male end.
Yes, you can use this for that application.
No, this is for LP use only.
It is not recommended. It is for water, using it for other than that will cause damage to the item.
Yes this will work for that application.