You might consider a composting head such as an Air Head....A few illegal discharge tickets will cost you more than either a retrofit or a composting head.
Tell that to all the AirHead (which, btw, is NOT a composter, but a dessicator) owners who empty their urine jugs over the side instead of carrying 'em ashore. In fact, I've yet to run into any who DO carry 'em ashore. I'm not saying there aren't any who do...just none I've ever heard of.
"But urine is sterile!" is their battle cry. Sterile or not, it's illegal. US marine sanitation laws prohibit discharge ("includes, but is not limited to, any spilling, leaking, pouring, pumping, emitting, emptying, or dumping") of ALL"human body waste and the waste from toilets and other receptables intended to receive or retain body wastes." That includes emptying a jugful of urine over the side in any US inland waters and any coastal waters inside the "3 mile limit"...and the fines are the same as those for dumping a tank or flushing a toilet directly overboard.
Dessicators and composters would lose about 90% of their appeal if owners could no longer get away with dumping urine jugs over the side and had no choice but to carry 'em ashore to empty 'em.
