What is the ruling on using and verifying the purity of similar items suspected of being impure, such as a tissue and a water bottle suspected of being contaminated with blood?

If you doubt between two vessels or two garments, one of which is ritually impure (najis), the issue is a matter of scholarly disagreement: Some say it is obligatory to avoid what you are in doubt about, while others say you should make an effort to discern (taharri) and use what you predominantly believe to be pure. Shaykh al-Islam chose the view that one should make an effort to discern and pray in one of them a single prayer. This applies when there is no whispering (waswasa); as for the person afflicted with whispering, she should turn away from the whispers and not pay attention to them.