This wouldn't work because the urethra is soft tissue. The urethra isn't a hollow tube: When fluid is not passing through it, it collapses. All the suction in the world wouldn't "open" the collapsed tube. The negative pressure won't even get to the bladder or sphincter muscle. You might get a hickey on your penis though.
No good for draining the bladder. Good for a quick kinky thrill though, so I'd say go for it!