I'm about to dig down to find the top of my septic tank as well as the two "Catch boxes" (or whatever you call them) that are apparently on either side and just a few feet away from the main tank. Each box is located on separate lines, each of which run from different houses: my residence, and my guest house--which is where the problem I'm tracking started. (Friend staying there, extended stay). Before I undertake this big job, I am seeking advice/guidance as I have never attempted this before and I can not afford to pay a plumber of septic tank co. Bathroom/toilet sludge started oozing out of a broken PVC cap on an upright access port in the 6 inch PYC line that runs from the guest house down about 80 yards or so to the main tank and the ante-boxes mentioned above. (The cap on the access port noted above had been broken for some time due to mower blade strike; however the guesthouse was not occupied until about a 2 years ago.) My resident friend was brae enough to probe with a snake down into the access port and said thereafter that he felt like he was "hitting something"--some kind of blockage. I bought a plumber's bladder which we then attached to a hose and fed into that line, running it downstream of the access port. Friend reported that it felt like the blockage had given way, at which we put a new cap on the access point and congratulated ourselves for fixing the problem. Guest toilet appeared to work fine. HOWEVER, my un lucky resident returned home a few hours later only to find that sludge had not backed up out of the shower drain and had covered a large area of the floor. He cleaned it up and then went at the pipe with the hose/bladder hook up again, saying that he used a longer hose and went farther down the sewer line this time--though not much more than 20 feet all told. Lo and behold, upon my return to my house, I discovered that sludge was now coming up through my lower story/basement shower stall and had fouled that quite well--did not run out of the shower footwell, thank goodness. OK, toward a diagnosis before I start digging: We were first planning to go back into my guesthouse line with our plumbers bladder and running hose hookup--until I learned that the previous bladder plunge of only twenty feet or so had apparently pushed sludge out of my tank and the catch box BETWEEN the main tank and my house, which is fully 150 yards from where the water hose pressure was applied. This seems to tell me that both my catch boxes and my main must therefore be filled to capacity and that the water pressure was skimming off a top layer of raw unsettled sludge and forcing it back up the feeder line into my house. Now, in this context...this does not quite explain how the sludge went back up the guest house feeder line, AFTER we had used the plumber's bladder and had put away the gear,thinking the job was done. Anyway: any insight into what's going on here--whether confirmation of my entirely unprofessional assessment mentioned above, or any guidance as to what else might be causing this to happen. I.e.: Do I just bite the bullet and get to digging? Or is there something I can investigate short of calling out the pumpers? If I end up have to call the pump truck, I'll have to dig down to find the tank top anyway. But I want to explore any other conceivable tactic up front before I undergo that time and expense. This system was put in circa 1990/92 or so. Main house was not lived in for about 5 years 2005-2010 roughly. Guesthouse not occupied at all until about 2015 or so. Thanks in advance for any helpful pointers here.