I have a bathroom that is usually odor-free but occasionally sewer odor creeps in. When it does, it’s usually not intense but on rare occasions it’s intense enough to smell from the next room.

Any ideas? ~~I cannot connect it with any activity.~~¹ It seems to hit randomly. Traps are good. It seems to close to the toilet connection to the pipework but there are no waste water leaks in sight.

Do I need to remove the toilet and dig up the tiles? I could hire a plumber to scope the drain, but that would likely cost more me digging up the bathroom myself. Should I look into renting a drain camera? Or would it make sense to rent an infrared camera and pour hot water in the drain?

I think the kitchen drains may be upstream from the bathroom.

¹ (update) the odor seems to hit after I run hot water in the kitchen just upstream to the bathroom.