There are a few different ways that you can find the plumbing diagram for your house. The first place to check is with your local building department. They should have a copy of the plans on file, and they may be able to provide you with a copy of the plumbing diagram. If they are unable to help you, another option is to contact a professional plumber. He or she will likely have a copy of the plumbing diagram on hand and would be able to help you out. Finally, if all else fails, you can try looking online for a plumbing diagram for your specific home model.