No valve will drain ALL the beer out as is....even the ball valves we add to our kettles and mash tuns leave stuff behind. But we minimize it as best we can by using a dip tube, like the one I show in my bottling thread.
I get an average of 52 beers out of my standard orange handled bucket valve by using a long primary which compresses the yeast cake and allows more beer to come out of primary into the bucket AND my dip tube. I leave about 4 ounces behind.
I do agree about having some sort of hop filter in it, but I've found that that seems to clog worse then a properly laid out dip tube with only the tiniest gap for the beer to flow through. Again I have found that long primary EVEN with dryhopping in primary tends to reduce the amount of hop goop carried over, though if I chose to rack to a secondary even as an intermediate step, that would further leave behind the hops, BUT would run the risk of oxydizing the beer....so it's a balance.
But really, the dip tube has worked successfully for me and other brewers for years. Even with the plastic valve....