Your starting point is having your G8F figure ready with the genitalia of your choice already on the figure.
Now it's when you load the wet geo shell on the figure. It doesn't matter which specific wet geo shell you load into the figure; this procedure works with all varieties.
At this point, you'll get your genitalia textureless (white color, like in the following screenshot).
To fix the issue, first you need to select the wet geo shell in the Scene pane. With it selected, open the Surfaces pane and locate the surfaces relative to the genitalia. Check the following screenshot.
See how the selected surfaces have the RSL shader applied by default? You don't want that. You want them to be MDL. So your next step is converting them to the Iray Uber Base shader. With them still selected, open the Presets subtab and apply Iray Uber base to them. Have a look at the following screenshot.
You can either double click it or right click and select 'Merge into scene'. Both options will do the same. Once the shader has been loaded, open the Editor subtab again and you should see this now.
Your genitalia will still look Off, though. But now everything's ready to do the necessary material swap that will efectively make it look absolutely fine.
Still with the wet geo shell selected in the Scene pane and the Surfaces pane open, now you should copy the torso's surface. Again, look at this screenshot.
And now the final step. Select all the surfaces relative to the genitalia and paste the copied torso's surface on them. Like this.
And that's all. After completing those steps, your genitalia should look perfectly normal and wet. Like this.
I hope everything's clear, English is not my language (I'm from Spain). If you still find issues, ask me.