There is a fowl smell coming only from the shower drain in the bathroom. The bathroom has not been utilized for 3 weeks. The flow is consistent and does not clog. What can be done regarding this?

Keep your trap wet meaning use shower often to prevent dry trap. Water inside the trap keep sewer gases inside the pipe and preventing them from entering room.

Try 1/2 a cup backing soda 1/2 a cup of table salt mix together pour it in drain and pour 1 cup of vinegar leave it over night, when you get up in the morning pour a bucket of very hot water and turn on your shower on the hot side for couple if minutes, I am sure this will help, thanks.

John