If I wanted to I could p@@ 4ft up into a water inlet-not bragging just a fact-However, last I checked, urine does not hurt anyone although it might amuse some.
That said there is a wasp here in the SW (maybe in the whole US for that mater) which makes a nest in small caliber holes, like the breather tube on the fresh water tank, I have had up to 6 inches of nest in my breather line. I use a brass gun barrel brush as a plug in the breather line for that reason. If I had a door on the inlet that would not be a mod I would have needed. So while not needing a lock a latching door might be nice.