Fridge , defrost water drain pan , and hose could be plugged , but should be cleanable .
Do you have access to compressed air ?
For tank clean out , both grey and black , get a big package of denture cleaner , drain the tanks then put in about a 1/3 tank of water in each , dissolve about 20 of the denture cleaner tablets in warm water and pour into each tank . Then go for about a ten mile drive, then drain the tanks .
You said 6 months in your first post , is this RV only six months old ?
Or have you only owned it for six months?
Because this kind of clean up seems excessive for a newer RV.