Occasionally in one of the bathrooms of my parents’ house, there is a stinky sewage odor. My sister has been trying ways to get rid of it, and even called a plumber last week. However, the timing of the plumber was out of the odor one, and he indicated no problem with the drain hole. He asked about the vent – it’s channeled to the terrace of the apartment and our flat is on the first floor, so ruled out. He also noted that there are water in the drain hole and that means, no smell/gas can enter.
He gave up, and so did we. We have no idea what could go wrong. My sister is fed up with the stink, and today after her expression of dismay I tried to read about the potential causes. It actually started with trying to find that patch like thing that fancy places use in the urinals inside men’s washrooms – yeah, they are called urinal cakes or urinal deodorant blocks. Searching more about the issue, I got to know about drain-trap and vent system of the plumbing.
So, the water that the plumber was indicating is precisely the water inside the drain trap that prevents sewer gas from exiting through the drain hole in the bathroom. The vent pipe prevents the water in the drain-trap from siphoning out (and thus not letting the sewer gas from below enter the drain hole). Ah, plumbing is entirely a pressure difference game! To understand this more precisely, I looked for resources, and found the International Plumbing Code (which also maintains various other codes including building and mechanics). Indian Plumbing Association (IPA) consulting with the International Association of Plumbing and Mechanical Officials (IAPMO) releases a regular code for plumbing activities in India. The recent 2022 version of it is a two volume illustrated edition which is quite good to read. Here is a snap from the vent (chapter 8) section of the book. The book can be accessed for free here.
It would be great if I can find a more professional plumber who can analyze the issue more closely and get to a solution. For now, I will try to look if the drain-trap is empty when the sewer smell is present. It has been clearly written in the code that the sewer gas is quite hazardous, and is connected to SARS! Anyway, too soon to conclude what’s wrong, and if the odor is even coming from the dry-trap – but this is something to definitely try fixing soon.