Let's try instead to think about how much this is going to cost in 20 to 50 years.
Let's use a boating analogy for perspective
I think long-term cost-based measures are really the only rigorous method of protecting the environment. Defining an actual monetary cost for the environmental impact, and then pricing it in, helps everyone make sane solutions. The obvious usefulness are cases where a small amount of pollution will create enormous value, meaning we still want to pollute, as long as the absolute quantity of all pollution is actually small. The result of a system like this is joe citizen or joe corporation can simply make the best economic choice, and they're also making a good environmental choice automatically. Cap and trade-type systems are a good choice, but there are others. The detractors for these types of systems generally aren't opposed to the economics; they're really opposed to the cause.
So none of this matters if people don't believe in the cause. Boaters tend to be a nature-loving bunch, but there's sure a lot of misunderstanding when it comes to environmental issues--and a good part of it seems to be wilfull.
An exemplary example is John Vigor's Things I Wish I'd Known Before I Started Sailing
, which I read cover-to-cover as I was thinking about buying a book. The book is full of good advice, but somewhere in there is some nonsense about (paraphrasing from memory) how it is probably OK to poop in coastal waters because lots of fish poop in there, and stuff. It's true, in the past six years, people have wised up a bunch about this sort of thing, but it's still nonsense, and could have confirmed it with any legitimate expert of his choice, such as an environmental engineer. Or jeez, doesn't this guy have Google?
To reply indirectly to Minnewaska, with respect, I think he's decided first that he doesn't want a gray water tank, and is then forming convenient rationalizations. Biodegradable soap? This is in no way helpful, other than an ineffective attempt at greenwashing. Biodegrading of soap doesn't help, because the base constituents that the soap would degrade into are still harmful because they inevitably upset the nutrient balance. And there will still be soap bubbles on the water until the stuff 'degrades.' This isn't secret information; responsible biodegradable soap manufacturers put this right on the bottle. Biodegradable soap is only meant to be used at a distance from bodies of water. This is what I mean by wilfull ignorance.
Please don't claim this has something to do with logic. If you've got some logic, I'm more than willing to examine your modus ponenses and demorganizations. No, the difference is of opinion is that you don't think the environment is worth protecting, or you personally just don't want to be bothered.
I'll be clear about what I want. I want water that is as practically clean as if humans weren't dumping their crap into it. I'm not opposed to small amounts of mitigated pollution, such as generated by carefully dispersed or treated effluent. Maybe you're OK with how things are now, with most water bodies being too polluted to safely cook with or drink from, but I don't think it needs to be this way, and it really isn't that hard: people just basically need to not dump untreated stuff into the water.