Please don't even think about going down into one of those drain pipes! Poison gas collects in pockets in them and it is deadly. It is also explosive and the slightest spark could set it off. Even the City workmen are sometimes overcome with poisonous gas when working on those drains. The sanitary sewer drain is the worse and it should be completely sealed except where it empties into the raw sewage processing plant. Storm drains on the other hand usually drain into holding ponds or reservoirs and are supposed to contain only water run off. But people pour all kinds of chemicals into them including household chemicals and even oil and gasoline. No telling what you might encounter in one of those drains. And, there's no telling what is in the water that runs out of the other end. I wouldn't go near one of those things without heavy rubber boots and one of those heavy duty filtration masks like they wear at hospitals in isolation rooms. When you get home you should rinse everything off and immediately wash your clothes and take a shower. A little over board? Perhaps, but you are risking your health and possibly the health of your family members who might become exposed to that crud on your clothing. Just think about it. JIMakaKs