Question: At the risk of potentially asking an off-topic question, I'd like to better understand the maintenance of a septic tank. I've never had one before and am unfamiliar with how to manage one. 

My primary question is: how often do septic tanks need to be pumped? We're looking to buy a 4/2 house with a concrete septic tank "supposedly" with a capacity of 2250. 

My secondary question is: how should septic tanks monitored? Just an annual scheduled service check-up? I don't want to spend money needlessly but also don't want to neglect something that needs regular attention.

Answer: 
MarkD already gave a really good by the book answer, but let me answer from the side of a homeowner who has had septic tanks for around the last 20 years.

The only time I had any maintenance/inspection was one time when my yard was getting really swampy. I had a septic guy come out and he pumped it rather cheaply, no permanent damage, no big whoop. Those Rid-X commercials with the bathroom full of backed up waste seem like an exaggeration to me.

We try to go easy on the chemicals, but we aren't that diligent about it. Definitely no drain cleaners, but chlorox goes in the toilets regularly.

One thing we do about 2-3 times a year is flush either some baker's yeast. It is effectively the same thing as Rid-X and much cheaper. I've also heard flushing raw hamburger (small quantities) is another way to get the bacteria going, but I'm a little nervous about that idea. I figure my septic tank gets enough hamburger the "regular" way if you know what I mean.
If the tank and drain-field are correctly sized for the home and occupants, it is designed to be pumped about once every 5 years. If you have more than 2 people per bedroom living there, you may want to pump it more frequently. Fewer people than bedrooms and you may not need to pump it as much.

You should have it pumped and inspected when you move in. If the septic system is more than 10 years old though, you probably won't be able to depend on the guidelines above. In this case I'd recommend you pump it 5 years after you move in (or sooner if you have more people), and have them give you an idea of what the sludge level was. You can then decide how often to pump it based on the actual functioning of the field and system, and your own habits.

The sludge layer should be less than 30% of your tank volume. You can measure this yourself with a pole and some cheesecloth attached along the bottom length - place it in the tank, and move it back and forth and side to side gently, then pull it up and you'll see the depth of the sludge layer. If it's 30% of the total height of the tank, have the tank pumped.