You need to contact the landlord wherever he/she may be!
If I was sent to your house I would not be allowed to do anything without the landlords consent regardless of who was paying!
A septic cleaner would be my first suggestion as they:
1 tend to be less expensive than a "Rooter" named company
2 usually will clean a tank if needed or rod the line from the tank back to the house if needed
3 Rooter named companies often do not clean septic tanks.
4 will usually easily find the tank.