In general, they are very basic, but suit their purpose. Each bathroom will consist of a toilet and a wash basin. The quality can vary depending on the type of train selected, and the class of ticket purchased. On some of the privately run trains between Moscow and Saint Petersburg showers may even be provided in some classes.

Generally, they are clean and stocked with soap and toilet paper, and they are cleaned regularly throughout the journey. They are not perfect though, toilets rarely are. The class you travel in will inform how nice they remain, and how long this is for. Third class carriages, for instance, can have up to 54 passengers to a carriage, and so first thing in the morning when everyone wakes up, they will be quite heavily used, and so more likely to run out of toilet roll.

Remember that on many older trains, because the toilet empties on the track, the bathroom facilities are locked for up to half an hour before pulling into a station, the entire time the train is stationary, and then for up to half an hour afterwards. This also means that there may be queues in the time leading up to these periods, particularly in second and third class. This is particularly important at border crossings as the train can remain stationary for up to six or seven hours! Be sure to check any schedule that is displayed on the bathroom door so that you can avoid these times. 

We recommend that you think about taking bottled water for brushing your teeth, your own hand towel, and even your own toilet roll in case the on-board provodonitsa have been unable to resupply the bathroom; this is particularly worth remembering in the busier third class, or at times when lots of people may use the facilities, such as first thing in the morning.