sed -n '/^### /p'
Then eg:
sed -nr '/^### /s/^.{4}(.*)/\1/p'
sed -nr 's/^### (.*)/\1/p'
sed -nr 's/^.{4}(.*)/\1/'
sed -nr 's/^.{4}//
sed -nr '/^### /s/^.{4}//p'
sed -nr '/^### /s///p'
sed -nr 's/^### //p'
Then eg:
(or without the redundant addressing, just:)