Can some sperm remain unejaculated in vas deferens after masturbation if yes is it harmful ? plz help?

some ppl confuse vas deferens/ sperm ducts with urethra which gets cleaned after piss but not vas deferens...vas deferens/sperm ducts transport sperms from the testis to the urethra..if after masturbation some sperm remains in these ducts will this cause any damage....plz help...this question is haunting me for a long tym...plzzz. help plzz.