Because you are self-employed, you would use the T2125 -Part 4 - Line 9270 - Other expenses (specify) to claim your laundry expenses. Keep all receipts in case the CRA asks for them later.
This form is found under theIncometab -Self-Employmentand you start from there. Please ensure the top part of that form is filled out correctly, otherwise, it will prevent you from Nefiling. Like dates, Industry Code, etc...