The bad news is that a few days after returning home, while doing a normal post-trip inspection, I discovered some water on the floor behind the pilot's seat, in the baggage area.  The more I looked, the more water I found.  It was behind the aft wing spar in the baggage area, in the tunnel in the baggage area, at the aft baggage bulkhead, and at the autopilot pitch servo bulkhead.  I soaked up the water with a towel and wrung it out into a bucket.  I collected about a gallon of water! 

 

So where did all that water come from?  I think it came from the tail and moved forward.

 

I have heard that the cockpit and aft fuselage are at low pressure during flight, so it's possible that the water was sucked into the tail through openings in the aft spar for the vertical stabilizer and the elevator bellcrank.  (I don't understand how that could be, but it's a possibility.)  The water would have collected behind a bulkhead until the water level got higher than the lowest opening in the bulkhead.  At that point, additional water would flow downhill to the next bulkhead, where the process would be repeated.  That's certainly what it looked like when I was bailing it out.

 

It could also have entered through those same holes in the aft vertical stabilizer spar while the airplane was sitting on the ground in the rain for 48 hours.  If so, it would have traveled forwards in the same manner as described in the previous paragraph.  It's hard to imagine that a gallon of water could have dripped into the airplane, though. 

 

If the water is entering the tail while the plane is parked in the rain, then drilling a drain hole in the bottom of the fuselage, at the first place the water will collect, would be one solution.  If it's sucking in during flight, that's a harder problem to solve.  I suppose I could put a drain in the bottom of the fuselage, with an opening fabricated so that it would suck air and water out of the fuselage, but I'm not sure.

 

Anybody else had this problem?  Anybody else solved this problem?