Is a place considered pure, and do you stop washing if you are unsure about the removal of an impurity after pouring water on the impure spot?

The question stems from waswasa (whispering of Satan/obsessive thoughts), so it should be ignored. To purify a hukmi najasa (impure substance whose trace is not visible, like urine), it is sufficient to pour water over it. As for ayni najasa (impure substance whose trace is visible), one must ensure that its attributes (color, taste, smell) have been removed. If there is doubt about the removal of the impurity, the default assumption is that it remains, unless the person is afflicted with waswasa, in which case they must disregard these obsessive thoughts.