I work at a public golf course and we can't seem to get rid of the horrible sulfur/sewage smell. It starts in the ladies restroom, from the shower that's in there but is never used, and spreads throughout the clubhouse by mid-day. Some days it's worse than others. A plumber told us to run the shower every couple of days to get the smell out. He said it was probably the methane gases coming up through the shower drain since it's never used. When we run the shower for about an hour it helps a tiny bit, but not enough. What can we do? It's so strong sometimes that it burns my nose just walking into the restroom!

Sounds like the plumber has the right idea, dried up trap under the floor. Try pouring a gallon of water mixed 1:3 with bleach into the drains in the floor.

Sounds like you need to dig up Tom's recipe for smelly drains. See https://www.askmehelpdesk.com/plumbi...room-6638.html If a trap doesn't have a leak, likely a few minutes of water once a week would maintain the seal.

Also, methane is a common component of sewer gas, but has no smell. Sulfur compounds do.

The trap, if present, may have a leak as suggested or it may be an old bag trap or similar and be actually siphoning the water intended to operate it out of the trap as you add water. You shouldn't need to run the water for long to fill a trap but the advice the plumber gave you was correct in that the traps water may be evaporating from the trap and causing it to fail. If, as you have suggested, the odor returns within a short period, the trap is leaking or is not vented properly and probably siphoning out the water intended to create the seal. Check the vent and make sure it is adequate and is isn't clogged and causing the siphoning. If the vent is okay you may be able to route a special type of camera intended for this purpose into the drain to view what lies under the floor before breaking it up. If it's an old bag trap I would replace it with a p trap if possible.

All of the above are good remedies... but I read in your post that the shower is never used.

If it's really never used, why not just shut off the water and put a plug on the drain? You can get an inexpensive expanding rubber plug (also used for sealing floor drains) at most building supply stores.

Yeah, it doesn't make the situation perfect, but you don't need to start digging up the floor either.

Down the road, if the shower comes back in to regular use, then excavate.