A pneumatic tire seater configured to seat a tubeless tire on a rim has a manual internal slip (MIS) valve mounted on the end of a tank. A nozzle is mounted on one end of the MIS valve, and the other end extends partially into the air tank. The MIS valve has a slotted chamber with slotted chamber holes, and a slip cylinder that fits within the slotted chamber and has slip cylinder holes. A compression spring in the MIS valve exerts force on the slotted cylinder, pushing it forward to line up the cylinder holes with the slotted chamber holes and release the high pressure air from within the tank which goes through the MIS valve and out the nozzle.