Most of the restrooms on Titanic were public ones. Generally, all classes of passengers and different departments for the crew had cabins laid out in blocks, and each block had toilet and bath facilities to reduce the amount of walking.
There were a few private bath rooms attached to passenger and officer's cabins, but only for the most expensive cabins in first class and the most senior officers.
If you look at the plans here: http://dsc.discovery.com/convergence/titanic/explorer/explorer.html you will find the location of every wash basin, bath and toilet on the Titanic. In 1st Class some staterooms had a washstand with one basin [Eg: C-76], others had a washstand with two basins [Eg: C-78, C-128]. No baths or toilets were located within the staterooms. They were all in separate rooms. Often the toilet was in a room of its own.
Sorry, I did not really know where to put this question, so I choose an already existing thread about bathrooms.
I can find lavatories/toilets and baths for most people on board. There are members of the crew I can not find bathrooms for. The mail clerks.
Which lavatory do you think they used? In any case it looks as though they would have had to go up stairs to find one. Did they use the one marked as "Petty officer's lavatory" or the same ones as the 3. cl passengers.
Peter, I think you will find that they would have used one in 1st Class. Either the forward men's lavatory on E-deck or perhaps the one on C-deck near their Dining Saloon. They had no access to either 3rd Class or other Crew areas.
You are right, they would have used the same stairs that passengers used to get to the squash court, that would take them to the E-deck 1. class corridor close to a lavatory. There was a door between that corridor and the 3. cl hall, but it was presumably locked.