Titan is not transparent by a long shot, but it's not completely opaque, as Vincent tells Jerome. However this was the common perception back in the 1990's when this was filmed and before the Cassini-Huygens probe got to Titan in 2004.
Artistic License - Biology: Unless there's blood or other stuff that's not supposed to be in there in it, Urine doesn't contain genetic material.
There will almost certainly be shed epithelial cells from the urethra in there though.
