> I have pushed a number of 3 meter long 15 mm copper waterpipe in the clay  
> here each within a minute.
> The trick is to move them up and down whilst pushing in.

I once did the same, let water run in the hole while pushing the rod up & down
Yesterday I told this to an electrican who built a few grounding systems.
He said that this isn't allowed, because along the rod would develop holes when 
the water has left, increasing the resistance
Not sure if that is just myth or truth, and if such an instruction exists.



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