Had similar incidents with our 2008 5th wheel with grey tank overflowing. Accidently not shutting the bathroom faucet off after going at night. Fortunately the grey tank backed up into the shower basin and we caught it before it overflowed. This happened 3 or 4 times to us. Finally I said to myself, we've been lucky so far but it may not continue. What I did to avoid the overflow possibility was to put an overflow hose of the top of the grey tank down through the belly to the outside where the hot and cold drain lines are. This have saved our bacon twice now. Traded in our 2008 and now have a 2017, had the dealer put the grey tube overflow in our new RV.
