This is simply another matter of training useless and jo....
There are two way to accomplish this particular task...
The first and, in most houses the easiest, have your partner run around and flush the toilet, turn on the dishwasher and washing machine, and start up the drip irrigation, all within 30 seconds somewhere around the 5 minute mark of your shower.
The second, which requires a bit of sneaky prep, is the gatorade method. Fill up an ice chest with ice and water, let it sit for a few minutes, and scoop a bucket of said ice water mixture. Carefully carry the bucket into the bathroom Very, VERY , quietly. Then somewhere around the 5 minute mark of the shower throw the curtain aside and hurl the ice water at your unsuspecting partner.
This is a very important ritual that will not only test the limits of your endothermic endurance but also the limits of your own interpersonal relational status, both of which are crucial to your ability to have a good festival experience.
Take this from an old eagle scout - - - Be Prepared