For this you’ll need 8 clay in total, as well as three sticks and 3 lashings. The easiest way to obtain clay is to create a custom island with 3 clay nodes and place it beside whichever island you decide to inhabit. Travel to that island and swim around the reefs amongst the coral and stone structures until you find them. You only need to harvest from two, but adding the extra one in map generation makes for a little easier time finding them.
Take the clay back to your home base (if you wish) and first build your furnace with 6 clay, 3 sticks and 2 lashings. Then craft your bottle with 2 clay and 1 lashing. Achievement should pop almost instantly.