After using toilet and shower for a few days you have to empty the toilet cassette and grey water tank. You also need to top up the fresh water tank. Most camp grounds will have a dump station you can use if you stay overnight. Also, many towns will have a dump station, most of the time owned by the local council.
After a few days using fresh water, you need to refill the fresh water tank. It’s easy and won’t take much time. This video shows you how to do it