Now is the time to test the group of fittings that connects to the right of the solenoid. This is really bad because you have to take off the whole back panel.
Well I took off the panel to remove the solenoid and I had to take a picture (second picture) what was behind the panel. (The solenoid was being held on by 2 screws.) So I took off the group of fitting and they look totally clogged with rust. The barbs are the same way. I believe the only way to fix this problem is to order a new part from Grainger.
90% of the time you can get the shampoo unstopped by using a welding tip cleaner in the little tiny hose barb. Next step is to remove the barb with nutdriver for a more thorough cleaning and flush it out. I don’t think I’ve ever had to remove the nipple/tee on the discharge side of the solenoid to clean out. But those are fifteen year old combo units, so a good cleaning may be in order.