Often confusing for the newcomer, here is a brief resume of the types likely to be found in motorhomes.
Cassette toilet: A fixed toilet in the motorhome with a removable box (cassette) to hold the waste. Some types have a built in water tank for the flushing water, others use the onboard water tank. The cassette is accessed from outside the motorhome and is carried to a disposal point for emptying. This is the most common type to be found in motorhomes.
Portapotti: Is a proprietary type of portable self contained toilet, usually in two parts, the top part comprises the bowl and incorporates a tank for the flushing water, tho bottom part is a removable waste tank that is carried to a disposal point for emptying.
Marine toilet: Is a fixed toilet that is connected to a fixed waste tank in the motorhome, flushing water is usually from the onboard tank. As the waste tank is fixed you have to drive to a ground level disposal point for emptying which is accomplished by opening a valve and allowing the contents to drain out. This type of toilet normally has the largest capacity waste tank and is often to be found in American motorhomes and some larger European ones.
Normally used in all systems, if only to mask the smell. The formaldehyde based chemicals (like the familiar Elsan Blue) are increasingly frowned on because of the damage the chemical can do to the environment, in fact their use is banned in Germany and some other countries. There are some 'green' alternatives that are acceptable.
A proprietary ventilation system available for the cassette toilet that means the toilet can be used without chemicals at all. The system uses a small fan to pull air down through the toilet as soon as the flap is opened, a flexible tube carries the air to the outside through a carbon filter fitted, usually, on the cassette door.
How can I keep my 'marine toilet' holding tank clean?
After emptying the tank, before leaving, put about 10 litres of water in the tank. On arrival at your destination flush the tank out. It's not always practical to do, but done now and again should keep the tank reasonably clean.