Perhaps this needs repetition: Both the Blue water seal and the PSS seal should be fed from downstream of the raw water pump before it enters the engine if too much pressure use a small inline thumb valve to limit the flow. Anything else is your own call and demonstrably outside what the designers and manufacturers say.
For both on a yacht engine at 1000 RPM should fill a coffee mug in a minute- not big volume and not high pressure.
I have tested these for many hours and on faster launches and modern yachts you can easily evacuate the stern tube . There is sound engineering and years of testing on the bench and at sea behind these products, why spend the money then ignore the written instructions?
Rant over I must be getting old.