pre - cum? Update ***

Can pre cum only contain sperm if the penis already ejaculated earlier and did not pee? So let's say someone had cummed then later had sex the pre cum could but not 100% contain sperm. Is that the only way for pre-cum not to flush the sperm out ? Because naturally pre cum would not contain any sperm right ? Because if it did the pull out method wouldn't even be an option because sperm would be realized really on? 
*** Yes I heard you can get pregnant from pre cum , but only if the man had already ejaculated and did not pee and had sex so then the pre cum could of stored some sperm? And then again it's had happened but not likely