I do not have inside smells. Seams the P-trap work good in the galley. The garden hose connection is open all the time (same as the shower drain). I would close the galley cutout valve while dumping the black tanks (I have two of them) if your concerned. One last thought, I full time up to 2-3 months in the same CG. If you paper towel your dishes prior to washing them you may not have to disconnect the garden hose and clear it (back flush). I do now.
Don & Dona W/yorkies Gizmo, Master Chief, & Tali
2011 Flagstaff 8528 BHSS 2015 Ford 6.7 XLT
2010 Full Timers & Still Going