Foul Smell - Sink vs Shower P-Traps
Earlier this year I encountered a foul smell inside the coach, and it seemed like it could likely be coming from the black water holding tank however upon investigation I learned that the water in the p-trap for the kitchen and bathroom sink had either evaporated and/or drained into the grey holding tank as we traveled.
I've since made it part of my routine to make sure there's adequate water in the p-traps for both sinks and it's my first line of defense if I detect a foul odor.
More recently however, I noticed a foul odor once again yet confirmed (through a smell test up close and personal with each sink drain) that the water levels in the p-traps was not the problem. I use Tank Techs RX for both holding tanks and feel rather confident in my methods to maintaining those tanks. After confirming that it wasn't the sink traps I was lead to believe there might be an issue with the components of the black tank/toilet etc. Nevertheless that didn't seem to be the issue either.
In the end, I smelled the shower drain (the shower has only been used twice) and lo-and-behold I found the source of the foul odor. I poured some water down the shower drain and have not had any recurring foul odors.
Now... It was my understanding that the shower drain is a waterless trap and I had therefore assumed that I need not maintain a fluid level in the shower drain. Has anyone else experienced something similar? Can anyone help me understand why a waterless trap would need to be flushed with water to avoid foul odors from the grey holding tank?
2016 Forester MBS 2401S