Originally Posted by babock
Only way that can happen is if you left a faucet on with your water pump on.
Yes - the only inlets for your gray tank should be sink and shower drains. There is no (and no reason for) a direct connection between fresh and gray water tanks.
If you think about it, if there were, then there would also be a direct path for gray water to get into your fresh water tank.
And that would be approximately bad.