You drink large amounts of water. Water is preferred to sugar infused drinks because of excess of sugar that can be ingested. Diet drinks are to be avoided too because the sweet taste can fool your body into releasing insulin, thus dropping your blood sugar. I always add grains of sea salt to the water to help my electrolytes stay balanced. Drinking large quantities of water without replacing your salts is very dangerous and people have died from that; so always add a little salt to the water to avoid Hyponatremia.
It is possible to drink water faster than the intestine can absorb it and is thus discharged, putting you at risk of an undesirable mishap (aka shitty pants). The water is absorbed by the digestive system and is brought into the bloodstream. The kidneys extract the excess water in the blood and release it water aka urine into the uterer. The uterer is lined with smooth muscle that pumps the urine into the bladder. At this point, the urine is now informally referred to as pee, piss, wizz or wee-wee. As the bladder fills, it grows upwards into the abdominal cavity while retaining a flat edge on the bottom where the urethra leaves through the prostate.
The bladder is made up of a type of tissue called transitional epithelium which is able to contract and expand, making the bladder a large elastic muscle. The tissue continues to expand, but can only expand at a certain rate. If the bladder is rapidly filling, the urge to pee your pants will onset sooner, even if it holds less pee. Squirming, twisting and the occasional deep-knee bend with rock-star style crotch-grabbing are all exercises to help the bladder expand so that there is less pressure on the bladder floor.
When you pee voluntarily, the bladder floor falls into a conical shape and the peeing process begins. The floor can also go down if the pressure is to high. These sphincters are controlled in part by the levitor ani. If these sphincters are defeated due to high pressure, pee begins to flow into the urethra. The first segments of the urethra are muscular and involuntarily pump pee downwards the same way arteries pump blood. I suspect that this pumping is what gives the vibrating sensation during peeing. These muscles are involuntary so, when this sensation is felt, a crotch-grab is in order and a rather painful high-pressure sensation is felt as the urethra pressurizes. As soon as you let go, the pee flows out and the pressure goes down. The deltrusor and levitor ani may have restored bladder sphincter integrity by then so you will only have a small wet spot, but if this is the case, you only have a few minutes before it happens again. Usually after a couple times, it will no longer restore and about a third of your bladder content will come out before you can stop it. You will feel completely emptied, but that is not usually the case. —