Thetford Aria Deluxe Overflowed on its own

I learned to take some actions and habits to alleviate flooding our motor home--(again). Did it once and we were in the coach, hooked up to city water,and did not know the water was overflowing the commode until DW waded into the bathroom. Now we never leave water on when we are gone AND we have a water alarm in the commode area so should any water leak a very loud alarm goes off. Battery powered Water dog alarms are avaliable at most ACE hardware storesfor $15 to $20. Probably best money you will ever spend. A friend who has experienced same says ;it is not "if" you get a water leak it is "when".