It is wajib [1] for men to make an istibra [2], that is, not to leave any drops in the urethra, by walking, coughing. Women do not make an istibra. One must not make an ablution unless one is satisfied that there are no drops of urine left. One drop oozing out will both nullify the ablution and make one's underwears dirty. If less than a palmful (if anything from the size of a pinhead to less than a palmful) oozes onto the pants, it is makruh [3] for one to make an ablution and perform salat [4]. If more oozes, the salat will not be sahih (valid). Those who have difficulty with istibra must put a cellulosic cotton wick as big as a barley seed into the urinary hole. The cotton will absorb the urine oozing out, which will prevent both the ablution from being broken and the pants from getting najs [5]. Only, the end of the cotton must not jut out. If the cotton wick is long and its end remains outside and gets wet with urine, the ablution will break. Shafi'is should not put cotton there during the blessed month of Ramadan; it will nullify one's fast according to the Shafi'i Madhhab [6]. When a Hanafi Muslim imitating the Shafi'i Madhhab in ablution and salat uses the cotton wick likewise, it will not nullify his fast.

[1] wajib: (act, thing) never omitted by the Prophet, so almost as compulsory as fard and not to be omitted. Wajib al-wujud: Being whose existence is indispensable and nonexistence is impossible.
[2] istibra: Lexical meaning of "istibrâ" is to exert yourself, to free yourself from something disagreeable or impure. In the Islamic branch of fiqh, it means "after urination, to make sure that there is no urine left in the urethra lest it should drop into your pants afterwards and dirty them and break your ablution." Istibrâ is done by gently squeezing urine drops out of the penis, by walking up and down for a while (about twenty minutes), or by lying on your left-hand side for a while. Istibrâ has yet another meaning in the branch of fiqh, used in matters pertaining to conjugal relationships.
[3] makruh: (act, thing) improper, disliked and abstained by the Prophet ('alaihi 's-salam); makruh tahrima: prohibited with much stress.
[4] salat: i) prayer; (with salam)= salawat; ii) ritual prayer of at least two rak'as; "namaz", in Persian; salat janaza: funeral prayer.
[5] najs: religiously impure thing.
[6] madhhab: all of what a profound 'alim of (especially) Fiqh (usually one of the four-Hanafi, Shafi'i, Maliki, Hanbali) or iman (one of the two, namely Ash-ari, Maturidi) communicated.