Can a urethral tube retain fluid for several hours?

Happy New Year! Greetings from the latest iteration of the Sovereign Independent United Kingdom (which now seems to be in four parts?). It’s not my preference, but that’s how it stands.

So, with the new year comes a fresh cage following lots of trial and error. For the past week, this particular one has been perfect across the board—day or night, easy to clean, and so on. It accommodates a tube (which can be removed only when the device is off).

Before acquiring this specific cage, I experimented with various lengths, three different types of tubes, and made numerous adjustments to find something that sits in just the right spot: uncomfortable enough to notice but secure.

Here are my findings: The most comfortable length is either 20mm behind the ring or positioned far back near the perineum. Therefore, for practicality considering potential UTIs, 20mm behind the ring seems ideal. The smooth black silky urethral tube offers great flexibility, while the clear tube provides a wider bore for urination. There are several grades of this tube available; the thinner-walled variety is more flexible and works well. A useful tip: use a pencil sharpener to bevel each end until the pipe sits flush with the nib/end. This prevents scratching. Some ends have smooth inserts, which I avoided because it’s best to have something that stays put rather than slipping off easily).

I thought sharing this might help others.

Now, regarding my question: I’ve worn the tube for three full days now, excluding nighttime hours, with no glitches or problems. It’s hardly noticeable. But… When I take out the cage to remove the tube, a burst of urine comes out suddenly. This can happen even several hours after I last urinated. My guess is that either urine gets trapped on the outside of the tube within the urethra but held back by the meatus. Or perhaps the closed urethra creates a vacuum effect, like a straw with your finger over it? Does anyone know? And do you have any advice for ensuring I’m completely empty after going?

Thanks very much.