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

We have a 31 gal tank on our 2014 Bullet 285RLS and yes, it is full in 3 days.. showers, face washing, teeth brushing add up fast,even with just 2 adults.. and we use disposable paper plates so not much goes into dish washing.. but 3 days is about max on a 31 gal gray water tank. We can get a week out of the same size black tank.