So with the magnetic and looting axe you must get like 8 to 10 potions at a time. Whenever you have such stacked potions, take them and right click on the other. For eg : if you have 8 potions in one slot and 10 in other slot.
Just take the one with 8 potions and right click on the one with 10 potions.
They will become 17 and you can continue like that.