All the sentences are fine.
It's an idiom that's been around a very long time! The "house," in this case, refers to the owners of the restaurant or pub or whatever.
http://dictionary.cambridge.org/us/dictionary/english/on-the-house
1. The drinks are on the house.
2. Beer is on the house.
3. You meal is on the house.
4. Dinner is on the house.
5. The pie is on the house.
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Are they all grammatical?
Why do you use 'house'? Don't you use 'restaurant'?
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