This was an amusing series of posts. Picked it up via my usual keyword alerts. I've done many interior french drains. Google searching will show plenty of stuff but to correct any confusion in this post, the french drain should drain into a basin with a sump pump. Cheapest I've ever seen it is about $30/linear foot (very labor intensive) excluding the pump...I would only pay that little if I weren't finishing the basement. In my area, the pump is supposed to discharge into the street (verified multiple times by multiple building department inspectors).
As crazy as it sounds, many of the towns in Hudson County, NJ have combined storm and sanitary systems. The stormwater actually connects into the sanitary system. This whole area is a concrete jungle so you can image the amount of water entering the sanitary system. It's disgusting and illegal by federal and state law but too costly for cities to fix. And yes, when it rains a lot, the sewers backflow like water mains. I've seen it firsthand on numerous occasions in numerous basements with uncovered cleanouts, etc. The situation is getting worse because of higher tides and generally higher levels of water. I'm very wary of finished basements in my area, particularly if you have any floor drains, basement bathrooms, etc. I'm hearing numerous anecdotes from the sewer company about more and more complaints. Nothing like neighborhood sewage mixed with stormwater in your basement...