Is it permissible to work on the plumbing of a hotel that includes a bar, knowing that if I do not undertake the project, someone else will?

It is not permissible to provide a hotel that contains a bar with health or central heating extensions, as this involves assisting in sin and aggression.

As for selling goods to the hotel, it is not permissible if the goods are forbidden, like alcoholic beverages. It is permissible if the goods are food or similar items that are not used to assist in disobedience.