I pulled the spark arrestor plug on my generator muffler and am running it under heavy load right now to clean the soot out. When the Onan manual says to use a 7/16" 8 point socket they aren't kidding. It is a 7/16" square head plug and a 6 point or 12 point socket will not work. Fortunately it is a brass plug and wasn't rusted into the muffler threads. I was able to get it out with a 7/16" open end wrench.
I am doing this over gravel since hot cinders on the ground or pine straw or leaves could ruin my whole day.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof