we bought a house last year built in 1979. i began having problems with slow drainage of the washer and kitchen sink about 4 months after moving in. the kitchen sink and washer water was draining out the pipe that the washer hose goes into. i rerouted the washer hose to a nearby garage sink and was careful when washing dishes so as not to overflow the pipe. no overflow happened when i used the dishwasher. this week we noticed sewage in the yard and opened the tank to see it was full. called and had it pumped. we thought there was a clog in the main line because clumps of grease would come up the washer pipe when we tried to flush it. we opened the only outside drain we could find and managed to get a TON of grease and junk out of the line, but the line never drained into the septic. we have come to the conclusion that there must be a greywater septic or drywell. while unclogging the greywater line i finally got through all the gunk and was getting black water coming out the drain pipe. i assume this was dirt? so the problem is.... how do i locate where this pipe leads. the pipe is cemented on my patio which then leads to a pool. i have no way to "probe" the ground to follow the pipe. i dont know if there is another tank or if it just goes to a trench and thats why the water was black. any ideas??? the kitchen and washer are still slow to drain! i think my septic failed because our softner backwash was draining into the garage sink also... it originally was draining into the washer pipe but would overflow as well so we moved it too.