Imagine this situation. A man finally achieves what he has been trying to achieve for long. When he gets the news, he is sitting in a restaurant. Elated, he asks the restaurant manager to serve all the customers whatever they want, and he will foot the bill for all. There is an expression to describe this free serving of food. It is something like, ‘the house is…’ Can anyone please suggest what is exactly that expression?
When the restaurant pays for the drinks/food, it’s on the house:
(of a drink or meal in a bar or restaurant) at the management’s expense; free.
The preposition on is used with whoever’s paying, so in this case you would say that the food is on him.