In reject rare draft each player brings in 45 unique rare cards, normally using what ever is the least useful but avoiding completely useless cards. Basically the 45 rares you are most willing to donate for this, while avoiding big bombs that will make 1 player just win all games.
In best scenario you should require that each player brings in at least 6 of each color so then you will have for sure 30 cards from each player that are not all White
Reject rare drafts are fun as the draft pool is very random and it’s missing all the common removal and boost cards.
Read more:
magic.wizards.com/en/articles/archive/feature/reject-rare-draft-2005-06-28
https://mtg.gamepedia.com/Reject_Rare_Draft
https://magic.wizards.com/en/articles/archive/feature/reject-rare-draft-2-2004-03-18
https://magic.wizards.com/en/articles/archive/feature/reject-rare-draft-3-2005-03-17
What’s the best discreet reject rare combo you would use, hoping to get both/all cards?
MTG blog 