Leave messages
I like to get up early and go out exploring when often my travel companion wishes to sleep in. Any message I wish to leave I write on a post-it and stick it to the lavatory lid. (toilet seat cover). This can then be read by my travelling companion when she gets up.
Lucinda, Bath, United Kingdom

First one up checks
With us -- two widows -- whoever wakes up first, asks the other if she has to use the bathroom. If she is not ready to then the first up gets to use the bathroom and have a shower. Then when she is done, out she comes and gets dressed while the other is using the bathroom.
Arlene, Boston, USA

Use a mini flashlight
As I'm a very light sleeper who, once awakened has difficulty getting back to sleep, I let my travel companion know this and we compromise on those nighttime bathroom trips by using a mini-flashlight to get to the bathroom and then by just closing the toilet top. Whoever gets to the bathroom first in the morning, once we're both awakes, flushes at that time with the toilet seat down. A simple compromise.

If I'm traveling with someone who goes to sleep earlier than I do because I want to read or organize the next day's plans, I use that same mini-flashlight to light my side of the room and keep my back to my travel companion. That also helps to shut out the small light.
Arlene, Bethesda, USA

No need for two of each
Share bathroom amenities instead of carrying two of everything -- ie two hairdryers, toothpaste, body wash, shampoo, etc. This lightens the load for both of you.
Susan, California, USA

She needs private bathroom
Travellers should be prepared to compromise. I remember once staying at a pension in Europe with a friend who refused to get a room with a shared bathroom. We ended getting a room with a private bathroom, but she paid the difference in cost for the private bathroom. We were both happy.
Daria, Vancouver, USA

Sleep closest to W.C.
I normally get up to use the W.C. two or three times in the night. I always ask for the bed closest to the W.C. This way there is less chance for me to disturb my travelling friend.
Alana, Rome, Italy

What's your bathroom schedule?
The first order of business when traveling with a friend is how long each person needs the bathroom in the morning or evening and plan accordingly. It normally works out well when traveling with a friend who likes to pamper in the morning, because I like to pamper in the evening. If we both like to pamper in the evening, then we set a little schedule and abide by it for the mental sanity of both.
Rebecca, Madison, USA

Matches help in the W.C.
I always carry matches and set them out in the bathroom. If you're sharing with another person, after using the washroom, light a match, hold it and let it burn for as long as possible. It clears the air of bathroom smells.
Susan, Davis, USA