Black water tank flush line pressure

I think you may want to invest in a pressure control device that is used exclusively for the black tank spray.  Your observation that the pressure should not be too high is something that many of us may not have thought about, but should have.  I've never used a pressure control device for the black tank spray, but as I think about your practice, I am realizing that I should have.  There are some pump out fresh water faucets that have some pretty high pressure water that could blow the plumbing apart.  Thanks for sharing your concern.