Is verifying the exit of pre-seminal fluid (madhy) after arousal by smelling the underwear, then washing the private parts and performing ablution (wudu') when its smell is present, a correct action? And how are clothes washed from pre-seminal fluid (madhy)? Is it by rubbing and wringing them, or by simply pouring water over them? And is washing with water alone sufficient without detergent?

Islamic law does not mandate sniffing clothes to ascertain the emission of madhy (pre-seminal fluid). The obligation, upon knowing that madhy has been emitted, is to purify oneself from it. If you are certain of its emission, then washing the male organ and performing wudu' are valid. As for purifying clothes from madhy, the majority of scholars hold that it is obligatory to wash them until its trace is removed, whereas the Hanbalis consider it sufficient to sprinkle water on them. When washing, it is not necessary to wring out or scrub the clothes unless the impurity is solid. It is preferable to wash them with pure water, and it is permissible to use soap after removing the trace of the impurity.