Pity the lowly public toilet, a redolent reminder of the failure of the best minds in urban planning to address the most fundamental of daily necessities. Millions have been invested in the facilities for collective relief. Often, they have become targets for graffiti, trash-can fires, furtive needle activity, commercial lovemaking, emergency baths, laundries for the homeless, and repositories of castoff diapers. Go to any city in America and ask whether it has fixed the public toilet problem, and most any city in America will hold its nose. Except Portland. Here, where just about everything is greener, hipper and more carbon-neutral, it was only a matter of time before someone came up with a sustainable urban toilet. It’s called the Portland Loo, and it may be the first toilet so popular it has its own Facebook page.