In order to keep sewage out of the water, you'll need some equipment on your boat. This fact sheet provides guidance about type and plumbing arrangements best for you. Recent articles in national boating magazines will also help. Allowable portable toilets must have a closed sewage compartment, particularly when being carried to the disposal location. Emptying the waste container isn't hard.
Some marinas have a separate dumping station just for portable toilets.
Others use their standard pumpout machinery with a different hose attachment for portables. If you cannot find an onshore dumping station, you can take the waste container home and dispose of the waste down your toilet. Just remember to dilute it, particularly if your home is connected to a septic system. You can also ask the marina if you can use their onshore restrooms. With pump handle in the off position, insert pumpout hose nozzle into deck fitting.