I would try to find someone to pump it out that has a smaller suction hose and try to go in either the inlet or outlet pipe. Something like a 2-inch hose should turn down when it hits the baffle, and should pump it out pretty thoroughly. The other option is to figure out where the tank is and core drill an access hole in the floor, if it's concrete, or if it's wood just cut a hole. After each pumping it need to be well sealed to prevent sewer gas from entering the room. If no inspection is required, you could get by for many years. We only spend 7 months in our primary home, and there are only the 2 of us, I'm going to wait at least 10 years before pumping again. When our 2 boys were home and we lived in that house year around we had it pumped every 2 years, but I'm not sure that was necessary. But, when we sold it, it passed the inspection!