The small hose is connected to full manifold vacuum on the engine side of the throttle plate while the large hose draws vapors from the crankcase thru the main body of the flame trap to the atmospheric side of the throttle plate. At low air flows/engine speeds the small line maintains crankcase ventilation under high vacuum, but it cannot draw large quantities of blowby air. At high speeds the air flow through the intake system becomes large enough to pull the larger masses of blowby air that flow then. The entire system is not connected to full manifold vacuum because this would lead to too much vaccum and then inward air leaks through the oil seals, along with poor airflow metering and driveability (opposite of what people have when the system is clogged).

The small hose can be replaced with any ordinary neoprene/rubber vacuum hose (thick walled) that will slip on snugly. The end of the large hose can be secured to the flame trap body with a band clamp if it gets stiff, or else you can force or clamp a short piece of rubber hose over it to extend it and then clamp the rubber hose end to the flame trap body.

When cleaning out the system I have found that the large hose can sometime have crud extending back into it an inch or more beyond the connection to the flame trap body.

Before replacing a suspect oil seal a person might clean this system thoroughly and observe the rate of leakage afterward. In my case I had leakage from the camshaft rear seals and it all but disappeared.