What you have is an "Extend-A-Flow" fitting, not an "Extend-A Stay" fitting. The port that's used to feed your grill will not accept the hose needed to connect an external DOT cylinder. You need the two port "Extend-A Stay" version and the POL hose that comes with it.
Dutch
2001 GBM Landau 34' Class A
F53 chassis, Triton V10, TST TPMS
Bigfoot Automatic Leveling System
2011 Toyota RAV4 4WD/Remco pump
ReadyBrute Elite tow bar/Blue Ox baseplate