Sewage Smell problems

Hi, I work in an office and we have two bathrooms. one we use as storage and dont use the toilet at all so there is no water in it. Well we came in this morning and it smelled like someone cut the cheese !!! I went next door to see if they had the same problem and they did. Well I called the property owner and then realized that it was coming from the unused bathroom for some reason. He came and said that it was because we need to flush that toilet every once in awhile, that the gases build up in the wall....is this true????