Hey Sue,
Just how do you drain a tank?
First we have to know what type of tank you have. A galvanized pressure tank or a bladder tank,(see images)
But wait!! This sounds more like a faulty check or foot valve that's allowing you to lose pressure as soon as it pumps up. This cycles the pump and it will not only send your electric bill skyhigh but will burn the pump motor out in time. I would just love to say that this is a easy repair for a homeowner but the foot valve's located at the bottom of the well And you'll need tools and some plumbing skills to replace a check valve. Call in a well or pump man before you need to purchase a new pump. Good luck, Tom