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

JFHenne wrote:
Nobody has mentioned the possibility that it is the tank sensor at fault and that the tank is not really full.

Yes I did. Back about post 4.

And I know that some people will find this idea repugnant but.....is really is not necessary to take a shower every day. Really.

It hasn't been that long ago that we didn't have running water at home and took a bath only once or twice a week.