Wow, some of these ideas. The hose will suck when PCV is GOOD. Breather hose forms first half of a loop which goes through air filter box, then hose, through engine and then PCV and hose to intake. When PCV is stopped up, breather hose will then show BOTH positive and negative pressure as pistons rise and fall, changing the area inside crankcase. Rising or positive pressure will be more because piston/ring seal never 100%, blowby makes more pressure than piston going back to TDC makes vacuum. This difference gets more pronounced as motor gets older, more blowby makes some oil mist go up that breather tube into air filter housing. Normal as long as it's not a lot. Entire PCV system works at a vacuum at low rpm/idle, but switches to more of a positive pressure containment system at higher rpm because vacuum drops way off at rpm along with attendant increase in blowby. The overflow pressure/vapor goes into the air filter housing to be burned. That's NORMAL. Not commonly known is the fact that PCV valves are (or used to be) often changed by Ford for ones with a different sized orifice in them to help accomodate the greater blowby leakage rates on older engines. They were called high mileage PCVs.
