Remove the base plug--part # 1249 on the exploded drawing in manual you can download from here:

http://www.raritaneng.com/pdf_files/ph_II/L04v0505.pdf

The cap should be in there between the bowl and the pump. Worst case, it made it as far as the joker valve, but that's unlikely 'cuz it would have to get through the flapper valve, which would (IMO anyway) would take more than just a half a pump stroke. No big deal to get it out of there...just remove the discharge fitting (part #1222AW) and grab it. If it's been longer than a year since the joker valve was replaced, this would be a good time to do it.