Just drop fertilized eggs from your inventory (not from your mount) close to them. They will eat it if not aggro on you, then use a mount they don't attack (rex, wyvern..). This week-end with x3, a big egg like rex, diplo or bronto gave 10% on a 140 and 145 so i think that the numbers (30) given by dododex are right.
Knock out it then place wooden spike walls around it then drop fertilized egg near the snake. When it will woke up, it will consume all the eggs and become yours. Please tap the good button to bring me happyand others can also see this tip.
You tame them by droping ferti eggs from your inv on the ground. You need to do so when the snake is not aggroed, so sit on a rex or smthing it wont attack. Be sure to drop them from your inventory, not from dino ones, that will make it bugged, it wont eat. To a lvl 20 Rex egg gives 29% on 2x event, bronto 26.7% and giga and wyvern the same, looks like all the big eggs give approxymately the same amount.. so dont waste the best you have ? If they get aggroed on you just run away and return, taming wont drop. Happy taming!