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Input from Bernd Material for sewer: I think you can get it very cheap if used or rest, maybe even the MST guys have it. Please check for KG 2000, the green one, must not be PVC https://www.ebay-kleinanzeigen.de/s-kg-2000-rohr/k0 or maybe there's even better stuff like Tonrohr that people do not like these days any more but that do a good job and will last 4ever.
Mapping
Matthias Larisch will draw the existing pipes on a map - this will be finished at 2012-12-27 (so if needed earlier or digging will start earlier, it may not help) as some measurements are missing.
Still the current connection to the rain well contains also connections that leave our ground. There are connections presumably to the garages as well as the not-anymore-existing buildings east of the station from the last spring well at the north/east end of the living building. That spring well contains only rain water connections and is connected to the next Gulli via DN120 (75cm below ground). That connection is not straight (maybe there is another hidden interconnection?) when looking at the tubes leaving both springs.
All the springs on the parking lot west of the towers are rain water sinks.
Our waste water sink connection is approximately in the middle of the plastered way. It is currently marked, but when washed away: Circle with 3m around the north/west outside edge and 6,50m around the north/east outside edge of the tower building. Dig 1,80m deep (which is approx. 40cm deeper than the existing waste water tubes)