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First thing is to determine the source of the odor.
Could be chemicals for the toilet. Many of us never add chemicals to the holding tanks, just flush with water. It this is the source, drain and flush, flush flush with fresh water.
It also could be formaldehyde. If so, getting rid of it will be a lot more difficult. Might do a google search for formaldehyde.
In general, the "Solution to pollution is dilution". Open windows, use fans to move air through. If you find it is something that can be cleaned off, do so and them more open air.
Dianne and Brett Wolfe
1997 Safari Sahara 3540
Moderator, FMCA.com Forums
Chairman, FMCA Technical Advisory Committee
Member, FMCA Long-Range and Development Committee 2007-2009
Moderator, http://www.dieselrvclub.org/(FMCA chapter)