We have a 10' quick-connect extension hose which has an integral on/off valve for our generator. The first time we used it, it took ages to get the gen started (for the propane to fill the line). So we got an extra male and put this in the female end fitting (so as to open up the line to gas flowing), and then opened all the master on/off valves until propane flowed freely out of the end near the genny.
Low pressure propane lines, it turns out, are very
low pressure, such that you can put your thumb over the open end, and stop the flow of gas by manual pressure alone (IMO).
When the gas smell was strong, we turned off the valve, removed the extra male fitting, and connected the line to the generator. After priming the carb, it usually starts after 3-4 pulls. And this is true even if we use 2 10' hoses to hide the gen behind the trailer, so it is at the quietest spot in the campsite.
PS -- FYI extension hose with shut-off:
Extra male: https://www.amazon.com/Camco-59903-P...Q9ANNEHF73QPCG