Rest stops in some states have them. Pilot/Flying J truckstops are actively promoting RV overnights and services and also have them. We generally go 4-5 days between needing to dump. Our new B will get us to a full week easily. And, of course, we don't stealth camp all the time. Our main preferences have been state parks and they usually have showers and dumps. Also, stealth camping at my son's house and other relatives' does not mean using the facilities in the van other than as a bedroom.
PS. If you go to Alaska you can legally pull over anywhere on the Alaska Highway or rest stops and pull overs in Alaska and overnight.