Just a simple fishing float i designed for someone, it actually printed really well so thought i would upload it. I made the bottom flat to make it easier to print and then just trimmed and sanded it round. There is also a dimple at the top so the model will be solid there to make the hole through, i used a small drill bit but I'm sure just heating a needle would work/

Print settings

Key is to print slow around 60-70% and then lower the speed even more at the top to allow it to print cleanly, on the Prusa i slowed it down to 40% at the top. It is a quick print so doesn't add that much time.

Print in Vase mode and enough bottom layers to allow you to round off the bottom, at a .15mm layer height i did 9 bottom layers.

Mine have all been air tight but could be painted to make sure.

Can try playing with the layer height but i found at around 0.15mm to be best.

I printed mine with a .6mm nozzle but I'm sure a .4 would be fine as well.

Post pictures if you catch anything lol.