My porta pottie only has a 3 gallon tank and must be taken ashore to empty. The rule is no solids so it is not too disgusting to empty, though sometimes it does become necessary to break the no solid rule and then emptying is disgusting. Since I am on Lake Michigan, I would NEVER go overboard, but I do know people who do. Another way to keep the contents of your tank to a minimum is to use a bucket, and again, I would NEVER do this, but I know some people who, when in port, use the bucket and surreptisiously dump it overboard. Most men don''t object to this method.
The porta pottie on my 32 footer has worked OK, but I am planning on installing a 20 gallon tank with pump out so anchoring out is not so challenging when dealing with solids.