Found a case of dialysis tubing sets dumped in a nearby field with some domestic junk. I'd guess someone on home dialysis died/was hospitalised and this was a house clearance. I put a couple of #22 needles with about a 70 degree bend in them through a washer built up from inner-tube rubber under the air cleaner hold down butterfly. The passenger side (blue) one runs into a bottle of fridge meltwater (I would normally use aircon condensate but its seasonally unavailable. Might have to distill for a while). The bottle breathes through an inline filter (referred to as a transducer filter in the dialysis literature IIRC). Dunno the specs of this filter but you can blow air through it. The idea here is that this will suck water so over time it will come to indicate/record the maximum negative pressure generated within the air filter. At the same time it should do some decoking, adjustable by the frequency and amount of topping up. The driver (red set) side is intended to serve as a real time manometer visible through the windscreen while driving and showing the current filter restriction. The set is bit short so I might have to join two together. The tape is unlikely to hold in the rain (dry season now) and there are likely to be ram or venturi effects causing errors, though these could be checked by disconnecting from the air cleaner. If I can find or make a hole I might move this inside, but since its mostly for initial evaluation I may just drop it. I thought of adding potassium permangenate to make the water level easier to see, but decided not to in case it got into the engine. Not sure when I'll next be driving the car, but when I do I'll let y'all know why it doesn't work. Bet you can hardly wait, eh? Alternatively, you can tell me why it won't work now.