Don't know about the black water flush.....others should chime in.
The fridge lites automatically. If the check lite comes on, that means it did not lite within it's alloted time. Turn the fridge off and back on, and it will try to restart again.
Wash the roof a couple of times a year. Recaulk as necessary.
If all electrical plugs and lights are working, then nothing needs to be done to the power converter. If something doesn't work on 120 volt, check the breakers. If something doesn't work on 12 volt, check the fuses. I have had 1 fuse blow in the last 2 years, and that is all that I have done to the converter.
Chap , DW Joy, and Fur Baby Sango
2017 F350 Lariat CCSB, SRW, 4x4, 6.7 PS
2017 Grand Design Reflection 337RLS