It's important that you can collect your wastewater when you're camping. Here you can buy both a tank or trolley for storing your wastewater.
At campsites you need to have a wastewater tank to collect your wastewater. The wastewater tank is emptied in a special container when it fills up. If you want to make it as easy as possible for yourself, buy a wastewater tank on wheels. If you already have a wastewater tank without wheels, the alternative is to buy a trolley in addition.