Submarine heads (toilets) are pretty simple in construction and operation, and nothing at all like most people are used to. In fact, the only resemblance is that they have standard seats.
They're of stainless steel construction, like many things on board a submarine. The biggest difference is flushing; rather than operating a handle like a normal head, there is simply a water valve that when you open it lets water into the bowl, and then you operate a large lever (about 3' long) which is attached to a 4" ball valve, which when moved manually opens the valve and lets waste drain to the sanitary tank for later disposal (overboard while underway to feed the fishes, and pumped to shore sewer lines while in port).
It's EXTREMELY IMPORTANT that all head ball valves are closed while blowing sanitary tanks overboard or to shore connections. Since the tank is pressurized with high-pressure air to force the waste out, the heads are secured and signs posted on the doors to warn crew that the tank is being purged. Failure to heed those warnings (or failure to hang the signs) has resulted in more than one unhappy crew member with high-pressure crap in the face as a result of opening the valve while the tank is pressurized.