For the solenoid valve used in your campervan for waste water disposal, it is indeed necessary to have a proper ground connection. You should connect it to the chassis ground to ensure safe and reliable operation.
Yes, it is normal for a solenoid valve coil to get hot during operation. The coil is an electromagnet that generates heat when it is energized. The heat is a result of the electrical current flowing through the coil. However, if you keep the coil energized too long it can lead to overheating and burning the coil.
