You know, one person problem, is another persons solution. In America, old toilets are problem. Millions, and million of old toilets are castaway each year, and what do you do with an old toilet? Until, the next ice age comes to crush the toilets into rubble, an old olive green toilet will be here forever.  There is also, the problem of sand sea bottoms.  Sand provide little, to no protection from the element in an ocean. often, a sunken ship, will provide a place for coral. Once you have coral, you ecosystem. If a ship will work, so will a thousand toilets.  Actually, toilets work well, but people consider them an eye sore, so there is opposition to dumping toilets in the sea. So, what  they do it, dump the toilets, in secert.  In the middle of the night, in secret location, thousand of toilets are being dumped in the ocean.  This is working so well, that small island are froming in the areas around the toilets. Where are they? Hell if I know. They don't even admit they are dumping toilets. The nice thing is, within a few years, the coral covers the toilets, and you can't even tell they are there.