Way of working among East Germans, a kind of infiltration (7)
I believe the answer is:
osmosis
'a kind of infiltration' is the definition.
'osmosis' can be an answer for 'infiltration' (thesaurus). I'm unsure of the 'a kind of' bit.
'way of working among east germans' is the wordplay.
'way of working' becomes 'mo' (abbreviation for modus operandi).
'among' means one lot of letters goes inside another (inserted letters are placed among others).
'east germans' becomes 'Ossis' (informal term for citizens of East Germany).
'mo' placed within 'ossis' is 'OSMOSIS'.
Can you help me to learn more?
(Other definitions for osmosis that I've seen before include "Absorptive process" , "Process of gradual absorption" , "XWD SETTER" , "Passage of bodily fluid through porous partition" , "picking up slowly" .)