Customer withdrew $10,000 from his account and cashed a $150 transit (not on-us check). For CTR #22, I would list his account but do I also need to use the + and leave the second "account number" blank or just leave it with just his account?

Part 22 only applies to accounts at your institution. List the customer's account associated with the $10,000 withdrawal. You do not leave a blank field for a not-on-us check.

Thank You Brian. I thought that since we would leave the field blank if all the the checks were transit that we would have to account for this in this case.

The only reason you leave the field blank when all the checks are transit is because you can't delete the field. There is no need to add blank fields as this does not add any value for law enforcement.