Finally refitting the headliner, I noticed the hose that carries washer fluid to the rear was abraded all the way through. That explains the stain on the old headliner. I cut out about 6" of old washer hose and spliced in some new hose and was ready to go but thought I should blow through that hose to make sure it was clear. No go. Looking at the little barbed connector at the back end of the headliner it is clearly more complicated than a straight thru filling which makes sense now that I think about it, without something in the line there all the washer fluid up in the headliner would continue to drip out. Now I am paranoid that it won't work so I want to test it before putting everything back in the car. The internet tells me it is a non return valve. I can't get it to open just with lung pressure. How do I test it?

 

Why don't you hold an air-pressure-gun to the tube at the front entry point and "shoot" air pressure thru the tube to clear it...?

PS: If you do not have an air compressor, try a syringe filled with water and press the water thru the tube from the front.

 

Thanks Peter! I had decided against the air compressor because my regulator only goes down to 50 PSI which I was worried would blow all the "guts" out of the little valve. I was trying to rig something up to the hand cranked bicycle pump but your idea of the syringe was perfect. Had one on my desk since I needed to clean my printer nozzles a couple of days ago so the solution was literally in front of my face. That washer non-return valve works perfectly. Thanks again for the suggestion!

 

Glad it worked out.

Yes, I know that the air-pressure from the compressor can sometimes be a bit much...:
To explain I have to define a word first: "tube": This is not clear in the English language: I am not talking about a tube, which is basically a pipe, and am not talking about the subway; I am talking about the tube, where e.g. toothpaste is in... - thus:
RTV silicon comes in a tube with a nozzle to be attached. I used the nozzle. After use I cannot close the tube, because the nozzle has no cap. So what to do to get the RTV back into the tube and out of the nozzle, so I can use it again next time? I figured to use the air-pressure-gun to transport the RTV back into the tube..
But that idea backfired - in the truest sense of the word: The tube opened up instantly on the back (it unrolled) and the RTV came shooting out with a bang and a bit was stuck to my trousers. I could not see any RTV elsewhere. Days later my wife complained about the orange "artwork" stuck to the door of the S-Type... So that's where the RTV came down... I had to scratch it of with my fingernails...