I think if you try to get most of the guck out the filters can pick up the rest. I do recommend getting a pre- pump filter as they too help suck up the sludge well and most can run good all winter. If you have a good pre-pump filter it will also extend the life of your pump as well. The type I have been using is well worth the money in my opinion, and I have used that type for several years now and am very happy with them. Now that my Koi have grown yet again, it is important to keep the water clean, so I have connected two filters together as my type of model filter can be extended quite easy.
I don't use any after pump filter, and never have, and a good thing too, as I now discovered many people with filters that are not underwater, have problems running them all winter. I am sure they work good during the summer, but never had any of those types, as I always just thought it made more sense to have the filter before the pump, so the pump would run better and not get clogged up. Plus I just hate the thought of anybody getting sucked up the filter. Many years ago, this greenhouse where I worked, used a big "sump" type pump that had no pre-filter and the fish used to get suck head first into the pump, and that really grossed me out bad, having to remove another poor dead fish out of the pump! I know that most big pumps now come with a cage of some type to prevent this from happening, and the Laguna big pumps have that round cage that works pretty good and does not suck up any fish.