Tank size should be in closing P/W somewhere. Bank usually wants a well and septic flow check done.
As noted, it depends on tank size, 3 of residents, and ground temp. Up here with cold ground, we have ours pumped every 2 years. I'm sure you could go 2X that.
Remember it is a septic system (poop processor) not a garbage can. I knew people that put every damn thing down their insinkerator into the tank. Chicken bones don't digest well in the tank.
