In my crawlspace-to-basement project I am to the point where I am installing the PVC perimeter drain before the concrete slab is installed. I'll have several cleanouts that will naturally have to travel through the slab. My question regarding those cleanouts is how close to the slab edge is too close? I'm thinking that there would be a point at which the concrete around the cleanout would be weakened and the risk of cracking goes up. The cleanout will be about 3.5" in diameter. Is there any standard rule of thumb on this? Thanks.