Most mucilages in nature are composed of glyco-proteins (complex molecules, put simply; part sugar-part protein), sundew dew, slugs and your nose all contain glyco-protein mucilages!
In plants the most abundant and common group and the one responsible for the sticky mucilage in sundews, are the arabinogalactan-proteins. their properties include an inherent stickiness and a high-water holding capacity. In Drosera the mucilage is produced by sub-cellular organelles, called Golgi Bodies, located in the cells at the tip of the tentacles.
I don't think the mucilage is particularly water soluble, it certainly doesn't wash of too easily in heavy rains, but don't know of any studies on it's solubility either.
Vic