Our flush spray nozzles were also on the passenger side in the Hydro Hot bay. I was able to access both, with a little soft language, and drill them out to larger size. Another tip I as told to try, is to:
1) Yep, the white vinegar and 1/2 cup of dish detergent, with about a 1/3 of a tank. Then drive for the day. I did this two days in a roll, with a drain and flush attempted flush in between.
2) Wait a good period of time between attempted flushing, to let as much water as possible dry out of the pipe line down to the nozzle. Then either white vinegar or even CLR (I used CLR) into the a small hose attached tot he flushers. Hold up the other end and use a funnel to get the CLR into the hose. I waited a minute or two to let as much drain out of the hose and into the pipelines towards the nozzle. Then wiped the hose coupling out with a clean wet rag, and used my mouth to blow some pressure into the hose too. (Note. This was a new out of the bag washing machine hose, not the normal hose I used for flushing
I then unhooked the hose, and put the caps back on. And let it sit until the next day. Then attempted to flush.
Even though I did these two steps, I also went ahead a drilled out the nozzles with the bigger holes.
The person who suggested these steps to me, said he had had reports back of about 25% success on the nozzles cleaning out some, as the hard water deposits were broken down by the vinegar in the tank. The CLR down the pipe line helped a bit more, and also cleaned of any hard water deposits off of check valves.
I have no input on your vent possibly being clogged.
Best of luck on this one! And, please let us know how it turns, or cleans, out.
04 Allure 40' Tag