This is my design for a simple 3/4" pvc end cap. The cap fits on snuggly with just enough room to add some adhesive.

Note: the inside diameter of the cap is 27.3mm and the outside diameter of the PVC I designed it for is 26.5mm. To get a more or less tight fit you may ave to adjust the scaling in your slicer. Consider printing a test ring just a couple of mm high and seeing how the ring lines up with your pipe.