Ah Yup! :0
We found a saturated roll of TP and some loose water on the head counter one time during our first full year of ownership, on our first "big air thrash" to weather... rail under sometimes... jib was really too big for the conditions but we were new owners and loved the power driving to weather.
That head sink and drain is outboard far enough on port side to allow a little gusher every time the hull gets pushed down. Ever since then we close that thru hull when sailing in medium or heavy air.
Good thing that the galley sink drain is close to center, and never has had to be closed when under way.
Love the O-34 aft head location and head orientation, but everything's a compromise.
When under way, bet you dog down the forward hatch, also.