Not the best photos, but some to give you an idea -
male mexican kingsnake side view - thick from the vent for quite a distance back - where the hemipene bulge is between two red lines
view from underneath - bulge between the two black lines
an albino cal king - not labeled but you can see the bulge in his tail after the vent (where the yellow stripe is interrupted)
couple pics of female corn for comparison - tail tapers sharply after vent, minimal bluge when seen from beneath (not the best female example, but only pic I had handy)
hope these help,
mary v.