Our home is one of those "older" ones, and yes, we have our grey water routed out to the ditch that runs along side our property. The drain pipe passes through a small concrete tank that is about 18" x 18" by about 12" deep (it has a metal lid on it about 3" above the ground level). I'm not really sure that it needs to be cleaned out because we haven't looked inside of it, in about 4 years. We built an addition over it. Before that time, we had live here 7 years and only looked inside it once in awhile. I'm not sure why, but we never had any grease build up inside of it. My thinking is that either we don't have enough grease in our diet (ha), or we have a lot of grease in our diet and we're eating every bit of it and not letting any of it go down the drain, or (more than likely) we have our hotwater tank set at boiling and the grease is still too hot to stick in the grease trap as it passes through that cold concrete.(posted 9673 days ago)I would put one in though. Our kids were always lifting the lid to show off the spiders and such inside. Having one will give you the pleasure of saying "hey, you kids, don't be playing in there!" or "put that lid back on there, before someone falls in and breaks their neck!" :-)