Every sperm is sacred, so don't spill any on the ground. (Or God will kill you.)
And Onan knew that the seed
should not be his; and it came to pass, when he went in unto his brother's
wife, that he spilled it on the ground, lest that he should give seed to his
brother. And the thing which he did displeased the LORD: wherefore he slew
him also. Genesis 38:9-10
If God doesn't kill you, then be sure to wash up thoroughly afterwards.
And if any man's seed of copulation go out from him, then he shall wash all his flesh in water, and be unclean until the even.
And every garment, and every skin, whereon is the seed of copulation, shall be washed with water, and be unclean until the even.
After washing up, pluck out an eye and cut off a hand. (It's better to lose an eye and hand than to have your whole body cast into hell.)
Whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.
And if thy right eye offend thee, pluck it out, and cast it from thee: for it is profitable for thee that one of thy members
should perish, and not that thy whole body should be cast into hell. And if thy right hand offend thee, cut it off, and cast it from thee:
for it is profitable for thee that one of thy members should perish, and not that thy whole body should be cast into hell.