Permits are usually required and fees exacted for opening streets, connecting to street sewers, and tapping water mains; and, so the question by whom the expenses will be borne cannot later arise, a clause is usually inserted in every plumbing specification explicitly stating that the plumbing contractor shall pay for and secure all permits. In the same section a clause is inserted making the plumbing laws and regulations of the city in which the work is to be performed part of the contract, in so far that the contractor must observe all such laws and regulations and install the work in conformity with them. This clause closes the doors on "extras" due to the fact that some work or material is not acceptable to the plumbing department, for the plumber, who should keep posted as to the requirements of the health and building departments, is supposed to have been aware of any difference between the plans and specifications, as prepared, and the plumbing laws, and to have covered him self accordingly by estimating on the method entailing the greater expense.