Something that occurred to me about Thetford Porta-Pottis -- before you use
one, open the flush gate and look inside to make sure the thing's not
already full.  Failure to observe this precaution can result in the toilet
equivalent of a LOCA (nuclear reactor Loss Of Cooling Accident)  because
there's a little vent in the top of the sewage chamber that opens along
with the flush gate.

:)
david
David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"