don't ask when was the last time we pumped the tank because we never DID! Hah! We moved in knowing we'd be demolishing w/in a few years. previous owner had just pumped it and said that was the first time he pumped in 25 years! Ahhh! so what's a few years? Everything's all clean so we can fill the old tank with dirt and put in a new tank. So, we'll be using again, maybe in another 25 years.