I agree it is worth a try with that configuration. The key will be the vacuum differential required to open and close the check valve.

My suggestion is to make a trial run with the tank sitting on the floor on the passenger side. That will tell you a lot. Tee a vacuum gauge into the line to the tank so you can watch what is happening. Find a long hill to climb while running the wipers.

If I understand your thinking, you want the check valve to close when the engine vacuum drops below what is in the tank. Then it should re-open when the engine vacuum goes above the tank vacuum. It should stay open under equal vacuum.

You are storing energy to run the wipers in the tank. It is functioning as an accumulator.

One scenario that will be interesting to observe is when you have depleted the tank and engine vacuum is still low. If things are working as I think they should then the wipers will operate (or actually not operate!) as if there is no tank in the system.

The next scenario to consider is what happens when the engine is trying to recharge the tank while the wipers are working. That might create a situation where the check valve starts opening and closing rapidly and interfering with wiper operation.

Great idea! I am interested in your results.

Rusty