Welcome to the Newschoolers forums! You may read the forums as a guest, however you must be a registered member to post. Register to become a member today!
*you don't use muscles to breathe in*
wrong. it has everything to do with the pressures being exerted on the body and the lungs not being strong enough to overcome those pressures.
some of the oldest scuba diving equipment pumped air from the surface to depths of up to about 60 feet through a hose/tube using manual pumps.
i've been a certified diver for over 15 years. my old man is an instructor and we run a scuba company on the side. (claim) I'm not going to argue with you over why you are wrong, just know that you are.
Problems design-wise, you would also have to make the tube so that it could be transported and it would have to stand up straight while you swam down thirty feet.