Depends how bad the scum is. Hot Sauce is great for doing the wipe down and getting the regular residue off the hull. If you have the real baked on crap it isn't going to cut it.
For that, try a product like Slimy Grimy: http://www.amazon.com/Slimy-Grimy-Sp...ds=slimy+grimy
On my old boat, the only time I left it in the water more than a day was at one of the nastiest lakes you can go to (Buckeye Lake in Ohio). Man made, 9' at its deepest part and most of it is 5', nasty, stump filled sewer of a lake with dead fish all over. After a week in that, I could not get the brown film off no matter how hard I tried...from washing it to a scrub brush to whatever other cleaning crap I had laying around.
Squirted this stuff on it, let it sit for a couple of minutes and rinsed the boat. It all just washed right off with just the hose. It is really good stuff. I'm sure there are other similar products to it but this is what I use. Not something I would use as a daily cleaner but great for those really tough jobs.