got any mates with car-friendly sized compressors you can borrow? One of the benefits of my hobby is EVERYONE has a compressor in their garage/shed/workshop for cleaning stuff! A little far for me to drop mine off though
It is much easier with a compressor without too much grunt - too much and you risk dislodging pipes on a lot of cars.
I had dodgy sunroof drains, but a happy side effect of pressure washing my car, including a good soaking with an under chassis angled attachment , was that it seemed to unclog whatever was stopping the water getting out.