some reference stuff-
My dirt-guy called 'em either blow-outs (or blowholes) or a suck-hole (water running into the tile at a place that wasn't planned).
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A little more to Theo's CSI advice. Some of this is addressed in the thread I linked above.
The clay drainage tile systems were often installed with inlets that have nothing visible at the ground surface. No pipes, holes, ducts, or (Bruce's favorite word) Hickenbottoms. The inlet is more of a French drain a couple three feet below the soil surface. It is usually a pocket of pea gravel over the opening in the tile, all covered with enough soil to run a disc thru without hitting the gravel. The only way to know where these are is (and this is the key) a) someone who knows where they were installed b) county drainage maps c) finding the low spot in a field that always collects water, has no visible drainage inlet, yet seems to drain much quicker than absorbtion and evaporation. If you can locate these inlet areas and face the pondsite, it might narrow down the subsequent
search zone.
Also, there is a probing tool that is nothing more than a T-handle with a 5' long hardened steel shank (about 5/16" dia) that you push straight down into the soil. At the business end of the shank is a embossed stratching surface. The idea is that when you hit something hard while pushing it straight down in an area that you think might be the tile, you can twist the T-handle back and forth a couple of times and the embossed scratching head will dig into the surface of the clay tile. When you withdraw the probe, you check to see if the head is loaded with red clay shavings. If yes, BINGO. If no, it might be tree roots or nothing at all if it was a rock.
