Hello everyone. I have a question regarding upstairs plumbing. I bought my house a couple years ago and soon after realized the bathroom upstairs (we rarely use) drains slow. And if we don't run water in shower odor comes up. I'm aware that the water in trap must be gone due to lack of use but figure it should take longer than a week to do so. My worry is that it may not be vented properly or not at all. Could some please help and give me some possible problems and solutions? Thank you all!

Suggest that you pour some cooking oil down the shower drain. That will slow down the evaporation process. If that extends the time before you have the odor problem again them the problem is probably just evaporation. If the cooking oil does not extend the time, then you may have a venting problem.

Suggest that you pour some cooking oil down the shower drain. That will slow down the evaporation process. If that extends the time before you have the odor problem again them the problem is probably just evaporation. If the cooking oil does not extend the time, then you may have a venting problem.

Thank you very Much. I was leaning towards vent just because of the drain issue. I will try the oil and see how things work. Thank you!