For some time, I had a weird feeling most times I prayed. Like urine was being released onto my clothes. But when I check my clothes after praying, I see no stains, so I simply ignore what happened.

But a few days ago, I had the same feeling when I was about to take a shower, so I was able to see if there was any urine. There was a tiny drop, probably not enough to make a noticeable stain, but urine nonetheless. I looked it up and it turned out to be a disease called Post Micturition Dribble (PMD).

A have a few questions:
1. Are any of mentioned prayers valid?
2. Are my clothes najis or tahir? Does it make them tahir to go through a washing machine? Or does it make the other clothes najis?
3. How accurate is this video? is using a cloth as avised allowed? What can I do to be more certain that if the urine leaves uncontrollably, it lands on the cloth?

1- Your prayers are valid since you don’t have 100% certainty that the drop of moisture is urine. It may be urine or it may be residual moisture. If you apply these steps after urinating:

Then you can consider the moisture pure. So don’t worry about previous prayers

2- You may consider them tahir since you don’t know 100% that it’s urine. Most washing machines purify the clothes if the machine pours plain water on the clothes at least twice

3- No need to keep a cloth close to it, because assuming urine actually out it made your body najes anyway…