If the tenant is "filthy"? due to a mental disability, then you need to proceed with caution to avoid any violation of the Fair Housing Act. Maybe G can give you the correct procedure required under law if this is the case with your tenant.
Some States do require a reason to be given for ending a rental agreement. This might be a requirement of your State?
You can look up Portland Oregon relocation fee law, new for 2017 which requires the landlord to pay between 2900 to 4500 dollars to ask a tenant to leave a rental house without cause in the case of a month to month. This does not include at the end of a fix term lease, a house shared with the landlord or the landlords own home which has been rented for less than 3 years.