This is a great solution for the z4 roof drain problem, 14mm OD Pvc tubing is a perfect fit for the grommet, I'll be adding some silicone to the plug before putting it in the hole. Then with the florescent pipe it's easier to spot a blockage. Run the pipe to the the splash guard drilling a 15mm hole with a hollow grommet and fit the cross section of the original drain valve at the bottom. This was help with debris getting back into the pipe.
