How do folks clean their hulls post-paddle? My Wood Duck tends to pick up a yellow-brown pond scuzz from our local reservoir. Sponging the hull with water alone I find, isn't enough to defeat pond scum, not to mention tiny nasty clinging bits of potentially invasive water plants I wouldn't want to transport to the next pond. But I am leery of putting soap grey water into a reservoir. Are there biodegradable, non-hurtful soaps or detergents?