wearhouse 6 building each has toilets their back to back each has 3in double tee main line feeds in to a septic tank i was told that the tank was drain but the to toilets at the in of the building slow going down i checked the roof vent and their is a 2in line from the 3in line 90s over then up i cut all that out to put 3in line stright up to vent right i snake the drain and still i see water in the line could it be because the 3in line going out to the far end of the building which those lines also vent thru a 2in line would slow down the flush to the last two toilets