Your Minnie has a 41 gallon fresh water tank that Includes water in water heater.
A black tank capacity of 35 gallons
A grey tank capacity of 38 gallons
Level indicators are junk (not just yours but majority used in rvs)
Please explain .......toilet would not flush.
Do you mean no water would come out
OR do you mean tank was so full that water was up to bottom of toilet.
Your bathroom sink MAY drain into black tank. Some are set up that way to extend grey capacity and provide more water to black.
Sounds like you just used more water than you realized.
Water running while washing hands, brushing teeth, combing hair, washing your face etc........shows up FAST because you have to collect it/dump it.
Showers? Lots of water if left running.
Dishes? Lots of water if left running to rinse.
Everyday habits at home show up when RVing.
2001 Minnie Winnie Brochure........
LINK