We recently bought a 4.8 cu ft washer to replace our old 3.7 cu ft washer. Our laundry is located on the second floor. About a month or so after the new washer was installed, we started noticing a sewer gas smell coming from the washer drain pipe. This doesn't happen right after a wash but rather happens after using the shower (following a wash). If I simply put some water down the washer drain pipe and fill the trap, the smell is gone. So it seems that the shower use (after the wash) is draining the trap connected to the washer drain. We have 2 full baths on the second floor. Initially, the smell was triggered after using the first shower which is closer to the washer. My thinking was that this shower's drain was perhaps clogged and so I unclogged it with Drano, hair removal etc. This seemed to take care of the trigger from the first shower but then the smell started to trigger after using the second shower. So I proceeded to thoroughly unclog the second shower drain as well. But the problem hasn't gone away. Now it is consistently triggering only after the second shower. It's interesting that once I manually fill the washer drain trap, the problem doesn't resurface until the next time we use the second shower - but only following a wash. I have checked visually checked that the dry vent from the washer drain and the two showers, isn't cracked etc in the attic and it seems to be connected to the main roof vent. I'm not sure what to try next. I'm looking for suggestions and would really appreciate any guidance/suggestions.