That "bleeder valve" is actually the "Fixed Liquid Level Gauge", and is not used to vent the tank other than the small amount that escapes until the liquid reaches the 80% of the water capacity point where the refiller shuts off the flow. On DOT cylinders, some states/municipalities require using the Fixed Liquid Level Gauge, while others require filling by weight. In practice, it's not uncommon to see refillers just fill until the OPD valve kicks off the flow, although that's not allowed by any responsible authority. That method is also used at times when refilling the permanent ASME tanks permanently installed on RV's without opening the Fixed Liquid Level Gauge as they should. The simple Fixed Liquid Level Gauge is far more reliable than the mechanically operated OPD.