Lining up small bottles of water, and other types of liquid, will be done, similar to the wettest link. That way, the girls can drink two or three per hour, spacing them out to avoid that bloated stomach feeling which usually stops them drinking.
If you are looking for the greatest capacity with this contest, a free pee might not be a good idea. It may also drag the contest on and on. I don't know how many of you want it to run for hours.
The girls are always asked to talk about how much they need to pee, but to do so for hours is a tall order. They run out of stuff to say. I would encourage them to mention it intermittently and leave them free to talk about other stuff, but that could be absolutely anything.
Comfortable clothing presents a problem. Women seldom look sexy in casual clothing - not impossible, but perhaps less attractive. That may have a negative impact on sales. I suggest anyone who has an opinion on this should speak up. Where there is silence, I will end up doing whatever I think is best, which may or may not be what you want to see.