Had my first major TM problem today in four years and it was really self inflicted. Went to replace the exhaust gasket and the bolt snapped off. £300 for a new divert exhaust but £75 to get a local metal fabricator to redrill, thankfully. I had set aside the day for maintainance so all was not lost.
My Boxer uses about a full tank for a suite. Sometimes even a full tank on a dirty 14x12 lounge.
Basically the more passes you make or the longer you stop wanding the more it uses.
However as Shaun says I hear the Alltec machines dump very little.
Dumping, noise, fixing it and fuel consumption are the only drawbacks of owning a TM.
MArk