We've tried camping with all the connections water, sewer and electric. That's called "Full Hookups"
All set up. Sewer, water and electric.
We've camped with water and electric. That's called "Partial Hookups" and means that the Sewer and Sink drain connections, called Black and Gray Water respectively have to be held in the tanks that are built into the vehicle and they have to be emptied manually. Overfilling the gray water can have water backing up into the shower pan which is not usually a disaster. Overfilling the black tank has sewage overflowing which IS a disaster and a very smelly one!
To empty the tanks you have 2 choices. You can drive the vehicle to a "Dump Station". Most campgrounds that only have partial hookups have such a station somewhere on the premises. Or some places have what's known as a "Honey Wagon" which is a service that comes by your campsite on request and hooks up your tanks to his big tank and takes away the stuff you don't want to think about! Good thing about the Honey Wagon is you don't have to pull in the awnings, disconnect the electric and water to go to the dump station.
We've also camped without any connections at all. That's called "Dry Camping" or if you are somewhere remote "Boondocking". Variations on the theme are staying overnight at places where it's permitted such as some Walmart locations, Cracker Barrel restaurants, Truck Stops etc. There is a whole subculture of Boondockers with websites and cell phone apps to share good locations. In order to Boondock you have to bring along your own water too and the vehicle is equipped with a fresh water tank. Hopefully the manufacturer calculated the sizes of all the tanks so they last about the same time before filling up. Our rig has 100 gallons of fresh water, 40 gallons of black water and 40 gallons of gray water capacity which is good for about 4 days.
Boondocking in the desert with Toyboxes full of ATV;s etc.
Having said all that and tried them we are happy to camp with whatever is available. If we are going to Boondock though we have to think ahead and fill the fresh water tank before we leave. We don't travel with it full normally because 100 gallons of water weighs 800 lbs (close to 1/2 a ton!) and we don't need to be dragging that up and down hills.
We (For we, read ME) screwed up last weekend. We were staying in a full hookup site but only for 3 days. Generally when you set up for full hookups you connect the sewer hose to the rig and put the other end in the sewer drain. The black water tank valve is left closed so that the tank fills with ... well you know what a sewer tank fills with!! The reason for letting it fill is to keep the solids in suspension in the liquids in the tank. (I bet you just put you breakfast sandwich to one side right?). When the tank is nearing full you open the drain valve and the contents drain out. You can do this as many times as is convenient. The gray tank valve is usually left open, it's just soapy water so it flows right out. The day before you want to leave however it is good practice to close the gray water valve for a day to let that tank fill a little. The reason for this is to use this water to flush the sewer hose before you put everything away.
In our rig the grey water valve is on the left and the handle is gray.
Note the clear plastic section in the hose so you can tell when the tank is clean after it gets washed,