I have a 1,250 gallon tank, 4 people (2 adults, two kids). IIRC when I looked it up, online said I could go 5 years. But the service I use seems to want me to pump every 2. Seems often, but with two women in the house (ahem) it seems inevitable. No food goes down our drain either. I tried looking into the tank, last time it was open, but I couldn't see what they go by. $320/pumping, vs what is probably $10k to replace. Kinda hard not to get sucked into frequent pumpings.
Don't quite understand why they use bedrooms online, it's really the # of people, if not simply how much they flush. I barely count in the calculation, since I'm away from home half the time anyhow.
The guy who does the pumping always tells me he has a list of recommended toilet paper. I always demure, as I'm not the one who has a vote on that stuff. Baby wipes should not go down the flush; but they do seem to cut down on the paper going down the drain (just change the bathroom trash more often).