Joining the shapes
Most of the modeling is done, but this mug is not quite ready to print. The body and handle are still two separate pieces and the bottom of the body, while flatter, isn't quite flat enough to trust to printing. We will be making some changes that will make further editing difficult so first we will make a duplicate of the mug's body easily modifiable objects.
Even though it's only been a while set another save point (Press F2, then Numpad +, and click on Save As Blender File) now.
Carry out the following steps to make a duplicate of the mug:
Center the view on all visible objects (Shift + C).
Select the mug body (right-click).
Do not touch the mouse.
Object | Duplicate or press Shift + D to begin the duplicate operation.
If the mouse is moved the duplicate will move which can be useful at times but do not move the mouse this time.
Press Enter to end the duplication operation.
With two identical shapes in the same location it can get confusing to select the correct one, so we're...