Is it normal to fill up the grey water tank this fast?

Ron Schulz wrote:
Sure you are. The only other explanation is you didn't completely empty it the last time you did it.

OR you are believing a status light that is indicating FULL a lot sooner than is true.

But you do need to radically modify your hand and dishwashing habits when dealing with limited water resources.......either the input or output.

I use zero water on dishes when in the RV. I use paper which I discard or plastic which I wipe off and bag to recycle when possible.