I just never heard of anything in the grey tank. The p-traps should keep any smells out of the camper, and the greasy, soapy water going down the drains should keep the valves lubricated.
If it has worked for you in the past, no use in changing.
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Chap , DW Joy, and Fur Baby Sango
2017 F350 Lariat CCSB, SRW, 4x4, 6.7 PS
2017 Grand Design Reflection 337RLS