Help With Turtle Tank Setup

I am new to the forum, so I apologize if this is not the correct place for this question. I have had a Map Turtle for a couple of years now. I have been battling smelly, dirty water for the entire time. There are periods where the tank remains clear for weeks and then other times the tank becomes so cloudy and smelly I have to change it in only one week. I have this new idea to help me do water changes and just make it easier to maintain. I want to make my own large capacity filter system and have it in my basement directly under my aquarium. I will plumb the lines up to my turtle. Can anyone please offer some advice on this?