Yes, to be fair, it takes no imagination whatsoever to work out the level of effort required to clean a uboat. As the parent of only one 18 year old, I can confirm, men in confined spaces, generate stench and mess

And yes, the armed forces treat cleanliness in super high regard, especially at the time penecillin was new and in limited supply.
I suggest the crews did clean, furiously, and in the endless entropy, they fought a losing battle so concentrated on the things that really mattered, rather than superficial looks. I dont think they had enough time to go through basic grime, think of all those oily handmarks on walls. Oil doesnt shift easy. And cleaning comes second to battle, so you can fall behind.
I shudder to think.