Remove your pork butt at least 30 minutes before cooking. Prepare the seasoning rub and generously rub the pork with it. You will have leftover rub that can be used to season the meat after cooking or stored for future use.
Add 1 cup of water to the inner pot and place the pork, fat side up, onto the rack or on a sling and place into the pot. You want the pork raised above the liquid. Put the pressure lid on and turn the valve to seal. Pressure cook on high for 90 minutes for a 7-8 pound pork butt. See notes for cooking suggestions for smaller cuts of pork.
When the time is up, allow the pressure to release naturally until the pin drops. Open the lid and remove the rack with the pork. Remove the liquid in the pot. I strain it and put in the fridge for other uses or to add some of the fat and juices back into the meat after pulling.
Return the pork to the inner pot. I put it directly in the inner pot so there is enough clearance between the crisping lid and the top of the pork. Close the crisping lid and air crisp on 300°F/150°C for 1 hour. Check on it after 30 minutes to make sure the top isn't getting too dark. It has taken 1 hour every time to render and crisp the fat cap, but I still like to check on it.
Remove the pork with meat forks or shredding forks and place on a cutting board to cool. When it is cool enough to handle, pull the meat off and shred into the size pieces that you want. The meat should pull off very easily. If it doesn't, take the crispy top off and PC for another 20-30 minutes. If you are using a bone-in pork butt, remove the bone and discard.
Season the pulled pork with extra rub if desired or add your favorite bbq sauce.
If you are not planning on crisping the pork after the pressure cooking time, then you will want to increase your PC time by 15-30 minutes. If your pork butt is boneless, I suggest adding 15 minutes to the PC time, but the air crisping time remains the same. Here are suggested PC times based on weight of pork butt
2 ½ pound pork butt takes about 45 minutes on high pressure with a full natural release
4-5 pound pork butt takes about 60 minutes on high pressure with a full natural release
6-7 pound pork butt takes about 70 minutes on high pressure with a full natural release
7-8 pound pork butt takes about 90 minute on high pressure with a full natural release.