In this screenshot of a Blender window, the two dotted lines originating in the bottom 1/3 of the image are tied to the couplers (the brown items in the mesh, for those who are not into things railroad). How can I get rid of the dashed lines, and keep the couplers?
I created the couplers as a separate mesh, and appended the libraries.
When you create an object, it has a “center.” That’s the large pink dot. As you edit the vertices of the object, you may move them away from the object “center” so that the pink dot is no longer actually in the center of the object. I’ve done that with both objects in the above image.
When you parent an object to another object, Blender shows this relationship with the dotted line (that’s what’s showing up in the bottom third of your image, and connects the two object centers in the above image.)
What you can do about the dotted lines:
Ignore them. They will not show up in your renders.
Recenter the object centers, so the dotted lines run from the actual locations of the meshes (and hiding the dotted lines inside the mesh where they won’t be so intrusive and annoying) Select the mesh and press Center New on the Mesh panel. Since the mesh is parented this will cause the mesh to jump to a new location. Move it back in object mode.
Join the coupler objects to the tanker object so they are all a single mesh. Select the objects, two at a time, and use Join Objects (Ctrl+j). There will only be one object, no parenting relationship, no dotted line.