[C320-list] Head leaks and cannot empty tank properly

[kspir4 at cox.net]

Hi Folks,
I recently bought a 2006 320 and have had problems with the head from the start.  Many of the problems seem to contradict each other and I was wondering if anyone could help.  First off, I rebuilt the Tetford hand pump so I feel that is working properly (flushing water comes in and waste goes out of the bowl).  I have been using KO solution to help promote decomposition but I don’t think that will help until the problem is fixed.  The symptoms (I know many of them seem to be contradictory) of the problem are:
1. Waste smell under settee and in the aft cabin.  I believe it is coming from a leak behind the head bulkhead.  I think it only leaks when I pressurize the system with the hand pump.  I do occasionally see some liquid coming down along either the pump out line or the vent line to the bilge near the waste tank.
2. When I use the macerator, it appears to be able to put a suction on the holding tank since it will usually draw out a little bit of waste.  However, at the end, it will always empty the bowl of any water that was in it.
3. I have tried to flush the holding tank by putting water in the topside pump out access but it will accept no more than a half-gallon before the tube is filled up and causing some liquid drip from the air vent.

I wouldn't think the air vent is blocked since I have some liquid coming out when I fill the pump out tube.  If that is the case, why does the bowl empty when I pull suction with the macerator pump.

There doesn’t seem to be any real inspection port to look into the holding tank for blockage or channels.  Is the only means to inspect the inside (without remove the tank entirely) to remove the small air vent port and look through that tiny hole? 

Is there an easy way to access the upper hose connections for the pump out hose and air vent to see where the drip is comming from and correcting it when found?  There appears to be an access panel above the shelf that is above the medicine cabinet but it looks like removing it would involve removing some factory caulking that seals the head.

Ken