Hello!
how do I put in the plant bottom of the elevation pipe and see also on the 3D model in which the elevation is located the tube?
If im understanding your question correctly, then...
First, you will need to make sure dynamic input mode is on (bottom left of your screen, its the one that says DYN, or if your in icon mode, its the + with a rectangle in bottom right quadrant).
Then when you highlight the pipe there will be a little pointy triangle (with point to top, make sure ucs is ste to world), if you click on the triangle then one of the pipe elevation dynamic input boxes will highlight the elevation (COP is default), you can then type in the exact elevation that you want for the centre of pipe. When in this edit mode, you can hit TAB to cycle between COP, BOP & TOP.
Hope this helps
Rich.O