It is a guessing game. Hard to know which pumps to get or how much that flow is going to increase. I can't see a feasible way of even calculating that, mainly because I still have no idea if this is a spring/storm drain or intermittent stream that goes crazy when it rains a lot. Or, it could just be rain water from the surrounding ground that comes in when the ground is saturated. Yeah, I looked into stuff like the french drains and other deep drains around the outside of the house a long time ago. Waterproofing in general gets up around the cost of a new car. These drains around the perimeter of the house seem to do the same, which is why those were written off. Average cost for a front and back yard regrade averages a $5,000 starting cost for pros. It apparently can double that in a hurry. Even after days of rain, usually the water flow stops a day or two after it stops raining and the pump quits coming on completely. Should I just not drill into the wall and just put sheet drain up as-is to redirect it? I'm not sure exactly why they made such a huge hole for a little water heater. This was before there was any system at all down there and there was just a floor furnace, so I don't understand the former owner's intent. A 15' long hole for a water heater that's maybe 2' across at best?