A stoppage-time free-kick from the England man rescued a point for the champions after Steve Bruce's side had lapped up plenty of pressure at the Etihad Stadium.
Manuel Pellegrini's side had been facing a third consecutive defeat on their own turf without scoring when David Meyler pounced on chaotic home defending to put Hull ahead.
And, having seen his side slip seven points behind league leaders Chelsea, Milner knows plenty of work is to be done if they are to retain their title.
Milner told the club's official website: "It's not good enough.
"I think coming off the back of a good performance against a top team [1-1 draw at Chesea] and coming here we knew we'd be up against a spirited side who were desperate for the points and we've slipped up again at home.
"You can look at a few things but over the 90 minutes I don't think we troubled them as much as we should have done. For whatever reason we've struggled at home this year and dropped far too many points.
"It's a flip from last year when our away form was poor. This year it's the other way around so it's disappointing but we need to regroup and come back and try and put a run of results together.
"Success in recent seasons has been based on solid home form.
"Last year, I think we drew one game at home, so that shows that we have to make the difference away from home now and can't really afford too many more slip ups - if any.
"I'm sure Chelsea will have a big lead now but it's down to us to concentrate on our game and see how many points we can get."
