I've found a big concrete trought under the shelters I have distroyed (need some more space for a vegetable garden).
Its weight is around 180 kg. Valerie and I moved it for 2 meters this afternoon, it took 2 hours!!
Now the problem is that the water goes trough the concrete, quite slowly but I think the trought will empty in 2 or 3 days.
http://croo.murgl.org/img/bac2.jpg
http://croo.murgl.org/img/xi-pelle-500.jpg