Choices:
A. Disassemble the bowl tail piece and pump when its empty and possibly containing the KO cap .....

B. Disassemble the bowl tail piece and pump when its FULL and possibly containing the KO cap .... while holding your breath while gaging and power-retching .... while spilling the pump 'contents' all over the place).

That cap is about 3/4" diameter and I 'think' the joker, etc. valves are a wee bit smaller in opening size than 3/4"