RV Repair: leak, freeway overpass, vent pipe

Question
We have a 2002 Fleetwood Flair 31A motorhome. We have a leak, apparently in the gray water system. We can see all the traps and drains from the kitchen, shower, and lavatory, including the vent pipe, and they are OK. The final length of pipe going into the gray water tank disappears under the floor and is not visible.  The tank itself is under the floor between the frame rails, and on a sub-floor, and doesn't appear to be accessible without cutting the floor. The leak seems to happen only when water is draining into the tank; and does not seem to leak when water is standing in the tank, although it has been only about half full. We hit a pothole on a freeway overpass in Utah, and noticed the leak afterwards. Any suggestions would be greatly appreciated.  

Answer
The pipes going into the tank are usually set up as follows and can cause some problems like this.
1. The pipe has a round base attached to the end going into the tank.
2. The round end is forced into the tank at an angle and then glued at that point to the underside of the top of the tank, this does not leave much holding area.
3. Some are just positioned in a bind on top and are lightly glued and are not permanantly attached.

It sounds as if your pipe was connected on top of the tank and has broken loose. If you can get to most of the connections at the tank see if you can move them easily. On the one that goes out of site see if it moves easily at the last point you can see or reach it.If they are broken loose then they will move very easily.