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CADman, on my 2011 325RLT 5th wheel the upper level houses one 40 gallon grey water and the one black tank. On the lower level is the 40 gallon galley tank. I would think that when draining the upper tanks, some black or grey water may seek to enter the galley and cross-contaminate if the galley valve is left open full-time. At least prior to dumping the two tanks on the upper level, you may want to close the galley valve. My procedure when dumping, with all valves closed at start: black first then rinse and close, then galley and close and finally dump the upper grey (shower water, cleanest of all) and use this to flush clean the pipes and drain hose.
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