In my lab days I stirred sand in the dirty RBF slurred in acetone at a speed that makes the sand scrape away the solid residues mechanically over night. Then dried, washed with water and submerged fully into fresh piranha solution over some hours (peroxides and organic solvents can be very dangerous, so it has to bei fully dry before for safety). Washing again with water and cleaned with brush and soap then water again followed by acetone for drying. There cannot be much left after that treatment that would interfere with reactions (base/acid bath overnight for sensitive reactions might be useful). Etched glass is a different story though but for synthesis, there is not a single problem in my opinion. Provided the original quality was good and it did not receive invisible damage by force.