how do i obtain the plumbing plot for my home in travis county?

I am needing to figure out where the clean-out is for my house. The city put in a new storm drain and the construction of it went through my property. They built me a new fence , but they also covered up the clean-out and now I need the plumbing plans for my house (built in 1969) so that I can do some plumbing work. Please help!