It wouldn't be too far off base to call pipe makers pipe sanders, as that is what a large chunk of pipe making time is spent doing! Sanding all the nook's and cranny's of a very detailed shape can get rather mind-numbing, but the results are worth it. There is not a lot to say in this section other than, be sure to sand ever little spot on the pipe with ever grit you use. Leaving scratch marks anywhere on the pipe is a big no, no.
The lowest grit paper I use is 220. I use this grit for the first sanding step, and I spend considerable time with this grit as I use it to do the fine tuning of the shape of the pipe. Coming off the sanding disc, the stummel with have humps and bumps and other surface irregularities. With 220 and patience, you can make the surface of the stummel perfectly smooth. I also use it to make all aspects o the pipe symetrical. Tweaking of the rim of the pipe to make it a perfect circle and other fine shaping tasks are things I do with 220.
From 220, I advance to 320, 400, 600, and finally 800. I have found that I cannot improve the finish by going past 800. Again, let me reiterate that you must be very careful to sand 100% or the pipe with all the grits. It is very frustrating to begin staining the pipe only to find a scratch that requires you to go all the way back to 400 grit to remove. When this happens you will have to resand the entire pipe with starting with 400 going up to your final grit. The reason being that you have to remove all the stain so that you can have a uniform color once you get back to staining.
Some folks like to apply a stain early in the sanding process in order to see such deep scratches and make sure to remove them early in the sanding process the first time around. I don't do his simply because I do not want any residual color left from that sanding stain. If you don't mind that little amount of color left in the grain, this is a very good way to be uniform with your sanding.