You have a 90 gallon Fresh Water Tank a 40 Gal Black and a 60 Gallon Grey Tank. Those were the tank sizes on Our 1990 Southwind and Our Sons 1989 Pace Arrow!
To super sanitize isn't Rocket Science. Figure 1 Teaspoon per 5 Gallons so 90 gallons will take a little less than a Cup of Chlorox! Use a Cup to cover all the pipes Fill it leave for an Hour or overnight , I run several sink fulls of water into the Sinks and shower and don't forget the Toilet! Also be sure to run it through both Hot and Cold lines Then Drain everything and refill with known good water!