Answer
(Fatwa: 691/510=L/1430)
If you feel wetness, check the underpants, if it is stained, wash the cloth as well as the private part. You should not offer salah without washing the impurity. This ruling is applied when the impurity is in size less than one dirham (coin). If it is spread in area more than one dirham the salah will not be valid. It is better for you to use toilet paper or clod after urination. Use water when you are sure that the urine dripping stopped. If the drops discontinue by walking, you should do so.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband