Some of the small units like class B's and some slide-in truck campers have cassette toilets. There's a 5 gallon tank you remove and take to the dump station. A unit that has a true black water holding tank either has a porcelin or plastic toilet. It could have a foot pedal or hand lever. Hope this helps.
Nearly all class A and class C motorhomes and the vast majority of trailers today have a tank to catch the "black water" which is the PC term for what you flush down. They use toilets designed for use in RVs which use much less water than a home type and also require a lower pressure supply. The two main manufacturers of them are Thetford and Sealand. When the tank is near full, you dump it into a sewer connection. These RVs also have a "gray water" tank which captures the water from the sinks and the shower. It too can be dumped into the sewer system.
My 06 Fleetwood Niagara has the hardwalled potty/shower, and the potty on it is a SeaLand Traveler-lite (made by Dometic - china bowl, residential style). You can view some of the potty's on the www.dometicusa.com website. This toilet has been a blessing - it's high enough for a semi-disabled (me) person to get up/down without assistance.