What generator do you have? We just had one installed this past Wednesday. You Onan RV Accessory PDF said this about ours!...
"RV QG 5500, RV QG 5500 EVAP, RV QG 5500 LP, RV QG 6500 LP, RV QG 7000, RV QG 7000 EVAP and Marquis Gold RV generator sets have a built–in USDA Forest Service approved spark arrester muffler. It is necessary to equip the generator set with a tailpipe at installation." ... It looks like most of them mufflers are built in!
2015 DRV 38RSSA
M2 106 Freightliner
HR Imperial 40' DP