What's pukka for jointing fittings (compression and straight threads)
for heating oil? I heard that PTFE tape was not OK. My Purimachos
green stuff says it's OK for oil but I wonder if it'd be that
effective - I don't think it gets thick and sticky over time like the
white stuff.

Also: it's a gravity feed system and it'd be easier to arrange the
pipework with a rise & fall to accomodate the filter and a butterfly
valve, as below:

________
| |
| tank |
|________|--- ___________
| ___?_ | |
| | | | |
-------------------------- ---| appliance |
|___________|

Should I have an air bleed at a high point in the pipework? (the point
marked ?)
Or should I try not to have a fall at all (do-able, but awkward).

tia

Stan the Span