When I need to pump out my tank, I go to a pump out station. After it's pumped out, I put three to five gallons of fresh water in the tank, and then have that pumped out. The macerator pump never sees this, because it's on a T off the overboard, and will only get flushed if I open its thru hull and run it. This would result in my pumping overboard from whatever is left in my holding tank. Even if I did this after I filled the tank with the above mentioned three to five gallons of fresh water, I'm sure what I was pumping would still be considered waste, and an illegal discharge. I would therefore have to be over nine miles from shore to do it. Which would take me a whole day. Which means there's really no practical way to accomplish it.
We here in the Pensacola area are blessed with miles and miles of protected waters, a huge bay, and numerous large bayous. There really isn't much need to go off shore, because there's nothing out there but more water, and maybe the thrill of being out of sight of land. Everywhere we could possibly go in the span of time we have available (a week or less, alas we have day jobs), from New Orleans to Appalachicola, is reachable by going east and west inside the barrier islands or along the coast. The only reason to strike out south and get more than nine miles offshore is to make the six to seven day passage to the Keys or Mexico. Or to flush my macerator pump apparently.
As the proud owner of a completeiy inoperable Shuflo macerator pump (motor runs, impeller is long gone, can't find a replacement parts kit) I'm considering the installation of a manual diaphram bildge-type pump in its place. It seems to me that it would be much more able to sit for long periods between uses, and at approximately 1/6 the cost of a similar electric unit (looks like less than $70 on this site) it would be well worth the inconvenience of having to spend two or three minutes manually stroking the pump to empty the tank on those extremely rare occasions when I'm actually legally able to do so.
And don't even get me started on the insanity of it all, where I'm considered an environmental criminal if I were to pump my measly 30 gallons of sewage into the bay, when the local utility authority inadvertantly discharges several MILLION gallons of untreated sewage several times a year. Regulations and fines are for the little people.