Yes - quite odd. The toilet on most TTs empties straight into the black tank because the BT is right against the underside of the floor between the frame rails and there is no vertical room for an offset run like in a 5er. If you can't see the bottom of the black tank through the throne, I would think that would be a problem.
Maybe the hole was not drilled through completely and the disc that should have been pulled out is now a flap still attached at one side. They arrive at assembly with no openings at all and all penetrations are made once installed in the unit.
2015 Rockwood Signature UltraLite 8282WS Platinum, GY Marathon LRD, TST 507RV TPMS
2005 GMC 2500HD CCSB D/A, Curt E16, Prodigy P2, Garmin RV760LMT w/BC-20 b/u cam