I use a sharpie, but the only one that’s ever lying about is light green, so hard to see on the bottle, and I usually just write two or three letters, thinking I’ll remember what it means. Then either I forget, or it gets added to or blended with others, and I have a load of bottles of unspecified liquid. I like it this way. I tell them apart by the colour, and by how much is left in each bottle. And sometimes two will end up switching with each other, when I confuse them, or when the level of liquid left overtakes another bottle I’ve not been puffing as much.
I filled the tank last night with what I thought was a caramel blend only to be surprised by ry4 (double maybe?) which seemed to have liquorice in it.
I wouldn’t be able to mix a small batch. I can only make small bottles of single flavours.