بسم الله الرحمن الرحيم
After urinating it is mandatory to make it sure that the drops have stopped, it can be achieved by coughing, walking a while, moving legs, lying for a while etc. During this you can place clay or tissue paper on the private part so that the drop is absorbed in it and after being sure make wudhu. If drops continued even after wudhu then wudhu will break and you will have to make again.
If the drop of urine spreads more than the depth of palm i.e. more than the quantity of one coin in the cloth (underwear) then it will be mandatory to wash the place, salah will not be valid without washing or changing the underwear. If the width of the urine is equal to one coin or less then you may offer salah wearing it but it is still better to wash it.
Sprinkling water over the cloth is for removing the waswasah. It does not turn the impure cloth pure.
Allah knows Best!
Darul Uloom Deoband