I want to share a method that I'm experimenting with and having some decent results. I have been mostly interested in becoming a bedwetter and have worn a diaper consistently at night for the past five years with little results. I can easily wet in any position, but for the most part, I wake up and have to consciously wet. I have also worn 24/7 for several extended periods, and am very comfortable in diapers. By concentrating on staying relaxed after urinating, I have some post-void dribble but no real daytime incontinence.
Over the years, I have experimented in holding to the point of uncontrollable wetting. This has always been very uncomfortable and I always worried about the pressure back into the kidneys. Recently, I began working on a modified version of holding that has been surprisingly successful. As a warning, this method still involves holding against a contracted bladder. The potential for kidney damage is still there, but I think it's less of a concern over time (which I'll explain).
Basically, you need to already be comfortable and secure wearing high capacity protection. Allow your bladder to become moderately filled, but not to the point of extreme urgency. The next step is to initiate bladder contraction. To do this, press firmly on the area just below your navel. When you find the right spot, you will feel the urgency in your bladder. This will take some trial and error to find the sweet spot. I use both hands to increase the area being stimulated. After you find the spot, press repeatedly about every second (kind of the same rhythm as CPR). Within a minute or so, you should begin to feel your bladder start to contract. Hold against this contraction until it passes. Relax for about 10 seconds, and repeat this process.
Each successful contraction becomes a little more uncomfortable. The goal is to wear out the sphincter muscle by straining against the contractions over a period of time. After a while, you will start to have little spurts that you can't stop from coming out. The decision comes in how long to hold against the pressure before finally releasing. This is where the potential risk comes in and you will have to decide how far to push it. I suspect that there is less danger than if your bladder were completely filled and providing constant backpressure into the ureters. (The periods of high pressure are just when you are stimulating the bladder to contract so I do think there is less risk than high capacity holding.)
Repeat frequently over the course of a day being sure to replace what you are urinating out, but don't drink liquids to excess. As the day goes on, you should find it harder and harder to hold through the contractions and the spurts of urine harder to control. Eventually, you will reach a point of no return and be unable to control a flood. You will also begin to have bladder contractions when your bladder is full without external stimulation. As your sphincter fatigues, you should find it harder to hold and for shorter periods of time.
The first day I tried this I wet the bed involuntarily that night. It was the first time in five years that has happened. I have been doing this every day for just under a week, and I've wet the bed consistently each night and slept through about half of those wettings.
The tradeoff is wearing daytime diapers. In order to keep the sphincter fatigued, I'm holding all the time until I can't hold back anymore. That is taking much less time on day five than it did when I started. I have no idea what longterm effects (if any) this method has. Potentially, it could lead to longterm OAB or overflow incontinence. It could also just be that everything would go back to normal if I stopped fatiguing my sphincter all day long. I've decided to keep it up for a couple of weeks to see how things develop.
Again, there are risks and it may not work for you as it has for me. One side effects that I've had is soreness in my diaphragm from clinching up while trying to fight through contractions. That has gotten better as the ability to hold has lessened.
I'd be curious to know if anyone else gives it a shot and how it works for them.