1. This coat is dirty with dust and mud. OK! 2. He never knows when Joan is going to leave, where she’s going, or when she is coming back. This one is OK but I would utilize the comma instead of using "or" so many times. 3. She just looks at him, a figure in the narrow hallway, dimly lit by the light coming from the bathroom. OK! 4. Eventually, he manages to form a sentence in his head. It’s not one of those three million sentences he has been thinking about for the past few weeks, not one of those sentences that have been breeding like wine flies over an open bottle of wine. I would change "manages" to "managed". If you want to keep "manages" then I would suggest changing "eventually" to "finally". So, to recap, either "Eventually, he managed..." OR "Finally, he manages..." good job!! these are very well written sentences!!

OK - with a couple of provisos ;^) In 2, you should probably have 'leave, where' In 4: where you have 'weeks, not', I would write either 'weeks. Not' or 'weeks, nor'. I also think you are stretching your imagery a bit. 'Breeding over a bottle' is a bit far-fetched!