Don't forget to include the water in the water heater whenever you add up total freshwater capacity, as water heater water is needed for various uses in the RV just as the water in the main fresh water tank is needed.
So, your Tioga probably has an actual 36 gallons of fresh water capacity .... 30 gallons in the main tank and 6 gallons in the water heater. You can even use the water in the water heater to drink if you leave the water heater off for awhile so it's water is cool when exiting any hot water faucet.