I bought a pair of epoxy syringes like these from Barlow's: https://www.barlowstackle.com/Flex-Coat-Color-Coded-Syringes-P1905.aspx
Their tip is tapered, so I drilled a snug fitting hole in the top of each component of the epoxy, and leave the syringes in the tops of the bottles.
When I want to mix some, I hold the syringe tight against the bottle, turn the bottle upside down, and pull out as much as I need. Then I turn the bottle back over, and remove the syringe from the bottle top.
Once I squeeze the first component into my mixing cup, I put the syringe back into it's bottle, and do the same thing with the second component. That way I never mix up resin and catalyst syringes, and they last forever.
It makes getting the exact same volume of components easy, and allows me to buy the bigger bottles of epoxy.