Septic tanks should be pumped typically 3-5 years.
If you don't know anything about the condition of your septic tank it is highly recommended to have it serviced right away.
How do you find a septic company? Contact you local county for a list of recommended companies that the county has already vetted.
Your not sure where your septic is? Neither does the septic company. Most of the time they can probe around and find it. However I recommend you get the plat for your septic from your local water and sewer department. It cost more if the company has to find your septic tank. So be prepared before you call and hire them to come out.
How much does it cost to pump the septic and clean the filter? Pricing varies from one company to another. Just make sure you get upfront pricing. If pricing seams really cheap, more than likely you will have some surprise cost come up that you didn't expect.
If they have to dig more than 18 inches to reach the septic tank there is additional cost.
Sometimes repairs are needed, so prepare for the worse case senerio and ask questions before you make the appointment.