Rainer,
A more difficult technical issue.
Here is a U 35 KTB entry somewhat related to the previous one:
"Nun wird folgendermaßen vorfahren: Diesel-, E-Maschinen- und Torpedobilge werden mit Hilflenzpumpe in die Regler gelenzt, um damit erst einmal Herr der freien Oberflächen zu werden. Aus den Reglern wird mit Hauptlenzpumpe nach außenbords gedrückt; so ist das stets schwierige Saugen der Hauptlenzpumpe sichergestellt."

which I translate as:
"Progress is made as follows: Diesel-, Electrical-Motor- and Torpedo-bilges are pumped via the auxiliary spring pump into the regulator tanks, in order to gain control over the free surfaces. The main spring pump is used to force outside through the regulators. The ongoing difficult suction of the main spring pump is therefore guaranteed."

Questions:
Are the "free surfaces" the same as the previous question - the bilge water above deck? Or are free surfaces in the regulator tanks the problem? I'd like to understand the motivation behind the unusual pumping operation, and why the main pump's suction needed to be guaranteed.
What types of pumps are used on board? Is "Lenzpumpe" meant to distinguish a spring pump from some other type?

Thanks again,
Hans