Answered by Shaykh Faraz Rabbani
If one has a doubt about something, how far should one go to remove that doubt if one can do so. Let me give an example: if a person has doubt that a small amount of urine has exited after using the bathroom, should one check, or should one ignore it? my point is, just because a person CAN check, should he check? or should he just ignore it even though he had the ability to check but just didn’t want to.
With issues relating to tahara, etc, one should ignore mere doubts. When there are ‘strong signs’ (and one is not prone to waswasa), it may be fine to check, but without being excessive about it.
2)what is the minimum allowable filth that can be left after istinjah when one defecates? Is filth that remains between the folds of the butt acceptable? What if its just a coloring (i.e. no “solids”) of filth that is visible if one wiped with a tissue? would that be enough to require istinjah?
5 cm or so in diameter, beyond the point of exiting. Less than that is sunna to remove, but excused if not.
More than that renders one’s prayer invalid.
3) does any removal of skin, without the release of blood, break the wudu? i.e. what if it was a big chunk of skin, but no blood flowed, would that break the wudu?
Falling skin, without blood flow, does not affect the validity of wudu. [Maraqi]