The trains in Japan always look clean, particularly the Shinkansen. At Tokyo station, the cleaners quickly board the incoming trains, perform a quick clean and have the train ready to go again.
The cleaners have special rooms and facilities which are actually located at the base of the Shinkansen tracks. You can see some of these rooms in the following pictures.
Can you see under the platform the area with the blue buckets? The cleaners can get in down here and walk around making it easy for them to move when the platform is crowded.