I once had a Weber Q that I wanted to be able to use for both the low pressure RV hookup and bottled propane. I removed the regulator from the Weber and installed a tee with a quick connect on the side of the tee and the original Weber regulator and LP bottle connection on the end of the tee. There was no need to install any gas cocks or any sort of bypass doing it this way.
Bruce
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2016 Rockwood Windjammer 3029W Diamond Edition
2015 Chevy 3500HD LTZ 6.0 Crew Cab 4x4 Long Bed 4.10:1 SRW