hi Wolf

It seems you have finally come to the "testing" stages of this U-boat kit?

You seem to be on the correct track with soap & water thing..but you need to
try and clean the resin hull with some Enamel Thinners all over the "dirty" marks
on hull. (do a test with thinners first in a small area). Also some needle files will come in handy for some putty work correction & another good (wet & dry) sandpaper job would be required before you are completely satisfy with your results??? Then you are ready for a light spray of PRIMER, after it is dry, another light wet & dry sandpaper job will be required before the two tone of greys finishing coats are apply to this kit... Use Enamel spray paints.

Hope this helps Rds, Joe Brennan