You said fiberglass so how about a long brush with soap and water unless the motor mount tube is cardboard? Kurt
Soap and water works, but it tends to make a mess. You do need a cleaning agent and some water to clean it up. I suggest trying the pre-soaked chlorox wipes taped to a dowel. I use them to clean up motor cases and the soot on fiberglass tubes. Works great and even the heaviest stuff just wipes off.
https://www.csrocketry.com/rocket-motors/motor-cleaning-brushes/cleaning-brush-38mm.html Chris has these in 29-98, I think possibly even 150.
https://www.csrocketry.com/rocket-motors/motor-cleaning-brushes/cleaning-brush-38mm.html Chris has these in 29-98, I think possibly even 150.
That's what I use and I'll even wrap the brush with scotch-brite pad to scrub the really tough stuff.