If the house and senate pass different versions of a piece of legislation, the differences will be resolved

If the house and the senate pass different versions of  a piece of legislation, the differences will be resolved BY A CONFERENCE COMMITTEE.
Conference committee is the committee of the United State congress which is appointed by the house of representative and senate to resolve disagreement on a particular bill. The committee is usually made up of the senior members of both house of representative and senate who originally considered the legislation.