Why does the mouthpiece and valve rotate and not stay in one place?
The valve pin was removed and not replaced. This is a small pin that fits into a groove under the bowl elbow. This is used to hold the valve in place for a table mount to wall mount. When removing the magnetic elbow, ensure this part is not lost. Place the pin in the center groove for table mount or a side groove for wall mount. See pictures under Basic Troubleshootin