Hey Graham welcome to dreamviews I'm afraid I'm no expert on WILDing but I think the emptying the bladder thing is just so it doesn't distract you. If you dont have to use the bathroom I dont think you should worry about it. Maybe when you WBTB you should try staying up a little longer and reading a book or something like that, this may help you maintain your concentration for your wild attempt. This hasn't worked for me yet but it does increase my overall awareness in the dreams afterwards and has taken me further into sleep paralysis then I normally go, just an idea. I'm still learning too but there are plenty of experts on this site, like dakotahnok, to help you out so feel free to ask questions