Does the defilement of the blanket and bed occur if pre-seminal fluid penetrates the underwear and trousers and appears on the outside of the trousers?

If wady (a thick white discharge) or madhy (pre-seminal fluid) is emitted after performing ghusl (definition) (ritual bath) from janabah (definition) (state of ritual impurity following sexual activity or seminal emission), ghusl does not need to be repeated. Outer garments are considered pure unless one is certain of their impurity, because the default state is purity, and certainty is not removed by doubt. It is obligatory to repent from the forbidden act of masturbation and to seek an alternative, such as marriage or fasting, and to occupy oneself with what is right.