Is this still added to the free dining plan, or do we leave the entire gratuity? We always leave extra, but would hate to see someone not get tipped right. I have done this work myself for many years.
Tax and tip are included whether you pay for the DDP or get it free. They state that it is 18% of what you actually order. If you share meals or order additional items, it is appropriate to tip an additional amount.
I'm not sure that 18% number applies to the non-Disney restaurants that participate in the Dining Plan. The gratuity is definitely included, but the 18% number isn't something Disney warrants as always being true for restaurants beyond its control.