Hi Prathamesh, thanks for your message.

To avoid a grainy surface it starts with the print orientation, further with condition and parameter of the machine. Also your powder condition will improve. After printing, if the part design allows, I would recommend tumbling. Here, different media leads to different results . If this is not available the classic needs to follow, which is manual post processing. For leakage proof, it needs to be a stable process but also wall thickness. You see, there are many topics. If you like discuss this in detail, don’t hesitate to sign up and book a personal meeting.
https://get.xometry.eu/sign_up
I would gladly discuss your points and answer your questions.

best

Niko