I guess it will be a combination. But when the engine is not running it will be the static pressure - which may increase on braking, but it won't form an issue at all
https://www.sensorsone.com/mh2o-metres-water-column-4-deg-c-pressure-unit/
There is no pump in the tank so the pressure will be max what the gravity produces (I think you also use the term "water column" for the pressure the fluid has when lifted above level and 1bar equals to 9.81 meter water column) so even if we count both the tank's level above ground and the height of the tank the top level will be less than 50 cm above ground the pressure will be less than 0.05 bar. No way it can push off the hose.
Mark, Can I have them? I hear you'll meet up with AB at Goodwood anyway, and then he'll sit on them for me. I would need your bank details or an email for PayScam /regin
You don't need a 100A alternator in a Seven. The Wosp can be adapted, but it's not a 1:1 replacement. Alan Bowler might know how it's done even without a multimeter and a wiring diagram.
You can always use brake cleaner to find air leaks. Spray it around the inlet manifold / hoses. If revs go up, you have a leak. Don't use it on the exhaust though. Then problem may be solved as the car will be written off in a fire!