The fly line companies have tested sinking lines to death. I think if you get a uniform sinking line it will pretty well sink tip first. What you could learn a lot about is leaders and these can be tested in a fish tank. Another useful thing you can test is how long the tip of the different fly lines will float. The chlorine in a swimming pool would bother me. I don't know what effect it would have on your test. Obviously it doesn't have the same properties as a fresh water stream. Whether it makes any difference I don't know.