Hi, Linda. I am sure not an expert on this but I do know that there is a reason why your floor slopes--or at least most of them do. Basement floors are normally sloped toward drains so that if you do get water in the basement, the water will run toward the drain. Realistically, most of us will have some water get into the basement. It is not really a question of if but when. I think that you have to take this into account when tiling the floor.