For residue that won’t dissolve, I use stainless steel wool. Break it into smaller pieces that will fit into the boiling flask, add iso and cap. Then a shaking method which uses the momentum of the iso to move the steel wool around the inside of the flask breaking free the residue. Drain the iso and residue, repeat as necessary. Then acetone afterward.
Take what the shake weight has taught you, but go a little more circular and you’ll get the hang of it.