When one wants to move ones hand to do a task, it is our conscious mind that wishes it but it is our subconscious that controls each and every muscle to do the task. The same exists with ones sphincters. As a result, to wet 'without control' as we wish, it is not 'without control' as it is our subconscious mind that does it. It is with control but not a concious choice. A baby does not care if everything s/he is wearing gets wet / soiled... all it does is sate a need to void. Yes, the baby will cry if cold and uncomfortable, but due to not knowing the action - result link, will not think that because it voided is the reason it is cold and uncomfortable.
To convince our subconscious mind not to inform our concious mind of the need to void, and just void takes a little coaxing. The easiest way to do this is to put ourselves in thick enough absorbent diapers with plastic pants, and plastic sheeting on the bed so even if we leak, nothing will get damaged. Also, as Bettypooh stated, our adult mind creates vasopressin to reduce the production of urine. This is to enable us to stay asleep overnight. The production of any chemical is expensive, and if the mind realizes that this is not needed - ie you are wearing protection, it will stop.
In simple terms, to regain subconscious control over our bladder / bowels, ignore all the signals and continue doing what you are doing whilst wearing thicker than normal diapers rather than using concious tricks to relax bladder / bowels. Yes, the first time will be difficult, but after a while, you body will revert to pre potty trained status, voiding by reflex instead of concious control. This will take a while until your subconscious mind is convinced, but once that happens, you will get the best nights sleep ever, you body will shift as it needs to to make voiding easier, and at that stage, can revert to normal sized diapers. Every other method is trying to convince your concious mind - which in reality, is not in control of anything without training.