This info I found on oscarfishlover.com... I know they are talking about fish, but this formula and technique can be used for axolotls too. Best of luck. :
Firstly, move the fish into a smaller tank, a baby bath or bucket - something that can be thrown away or easily cleaned.Put 3 drops with a half pint of water and shake very well, so the oil and water make a fusion - otherwise the oil will just float on top of the water and*for the euthanasia*to work the fish has to get the oil into its system. I must emphasise that it is very important that you mix the water with a clove oil properly to avoid it simply floating on the surface like any oil will.Add the mixture to the water that*the fish is in (1 gallon of water should be more than enough) and stir it around slowly with your hand. The fish should become lethargic and sleepy.Add another mixture of 2 to 3 drops of oil in water. When the fish goes "belly up" it is asleep - not dead.Then add 3 more drops of clove oil.* The fish feels nothing, it is very peaceful and humane. It seems mad that a few drops of something can have such an effect, but it IS very strong. Don't make the mistake of thinking that if you initially*put more in it will act quicker - it will only freak the fish out - it has to be done gradually so the fish doesn't notice the change in the water.
This procedure can take anywhere from 30 minutes, to a couple of hours, sometimes a little more. *If after one hour you still see some gill movement which indicates the fish is not dead, you can add a few more drops of clove oil. *Eventually, the fish will succumb to the overdose and pass away peacefully.