I think previous posters have diagnosed the problem correctly but want to comment on something you mentioned and that is the toilet fills to about 11/2 half inches below the rim. That's a nice thing to know about your boat!
I once had a boat that came with old heads that I soon replaced (actually just removed one of them) and I wanted to see what would happen if my joker valve failed someday. So, I opened the valve and let the head sloooowly fill until the water finally reached the rim, not good. So, I cut and routered the edges of a couple of layers of starboard plastic and inserted them beneath the head to raise it about an inch. Then, I once again tried my little experiment
and the head only filled to about 1/2" below the rim before the water stopped rising. I added one more piece of starboard for good measure and had greater peace of mind because I knew that a failed valve or seal could no longer sink my boat.
The reason I happened to think of doing this was that one calm, peaceful Sunday morning a few years earlier, while dinghying in to the dock
from my previous boat, a Hinckley Pilot 35, I happened to notice another Pilot 35 in the harbor that was looking VERY sleek, almost like it had been lowered.....it actually took a few seconds for me to realize that yes, it actually was a boat identical to mine..... and I couldn't see the boot stripe! Numerous boats were coming and going in the main fairway of the harbor within 50' of this boat, oblivious to the fact that it was slowly sinking right in front of them! I think the only reason I happened to notice what was actually happening was that I happened to have an identical boat so was very familiar with exactly how it should look. So, I climbed aboard and fortunately the companionway
was unlocked but the settee cushions
were already afloat so none of the thru hulls were visible, but because they were located in the identical position to the thru hulls on my boat I was able to find them and close them all so the boat didn't actually sink. I called the nearby Coast Guard station and the local marina and they both showed up with a big pump that quickly had her floating back on her lines. Work intruded
so I wasn't around the harbor much for the next couple of weeks. My mooring
was one of the furthest ones in the very outer reaches of the harbor and it was very gratifying about 3 weeks later to answer a knock on the hull
of my boat to see this eighty something year old guy (turns out he was quite wealthy and the Pilot 35 was his daysailor) in his little rowing dinghy
who was there to personally thank me for saving his boat. Apparently someone had told him I was the one who did it and he had been rowing all the way out almost daily to attempt to thank me.