This is the only type that is allowed on Ohio's waters. Types I and II are not allowed in Ohio. These types of MSDs are used primarily 3 miles from shore in ocean water. Type III devices include recirculating and incinerating MSDs and holding tanks. Holding tanks are probably the most common kind of Type III MSD found on recreational boats.
Sewage is stored in the holding tank until it can be pumped out to a reception facility on shore.
Their availability at marinas or other locations is largely a function of local boater demand. Most cruising guides and boating almanacs list the availability of pump out stations. An MSD is a special kind of toilet for boats. Toilets that discharge raw sewage directly over the side are illegal in state as well as federal waters.