I tried popping him the same way as the girls. With one thumb I pulled back the vent scale and with the other thumb I rolled from the tail tip towards the vent like a tube of tooth paste. One time I have something coming out but he started curling his tail around my finger and I gave up. The mass was coming out at the center of the vent but again not a definate gauge.
With probing I have watched a lot of videos. The likelyhood of causing damage because of a lack of experience makes me more comfortable with not knowing that trying to force the issue. At this point I have six sizes of probes and no idea what size is best for the appropriate snake. If I use one too small I am more likely to cause damage. If I use one too big it may stop short and give a possible false reading of being female?