I'm getting a hose from genos that will hook up to the shrader valve test port off of the VP44. If you go pre filter, you can't tell if the filter is clogged. If you go post filter and your pressure drops you have to change the filter to see if it's your lift pump that is causing it. Most will tell you post filter and that is what I am going to do. My hose should be here on Monday, so I'll let you know how it goes.