I'll let this post from the weddingbee.com boards speak for itself:
"Because this seems to be a topic that has several people hitting the panic button, here is how to pee while wearing your wedding dress:
On arrival at your venue
This ensures that you will not later get the train/back of the dress dirty just by having it touch the floor.
- Open the door of the ladies' room and look in. If the floor is not clean, call the venue staff and ask to have it cleaned.
- If the floor is clean, walk into the ladies' room and open the door of the handicapped stall. If the floor of the handicapped stall is not clean, call the venue staff and ask to have it cleaned.
When you need to go
You may now resume your panic about all the other topics for your wedding day."
- Walk into the handicapped stall. Remove (don't just pull down) your underpants.
- Facing the toilet, pull up the front of your dress to your waist.
- Walk straight forward, so you are straddling the toilet, and sit down that way. The train/back of your dress will now be away from the toilet, so you won't get them wet or dirty.
- Lean forward before peeing. That way, even if you drop the front of the dress onto the seat, you will not pee in its direction.
- 2dBrideAs a former maid of honour (aka designated-lifter-of-the-bridal-dress), I wish this sort of knowledge was more commonplace.