Greetings,
Mr. p. I hesitate to mention this but since it hasn't...Clean out that bilge cavity. One of the pictures shows a mess of black "guck". Aside from contributing to bad odours, it may hide potential pump blocking material (zip tie ends, dropped nuts/bolts or other detritus.
We always had water in our bilge (not a concern to me) BUT it was clean water. You might also think of installing a separate system for your shower water (container with separate pump).
I also notice soap suds in the area in one of your photos. I hope you are not allowing this to pump overboard as it is not terribly friendly to the environment. I found that when cleaning OUR bilges a wet/dry vac to be the best approach whereby any "scum' could be vacuumed up and disposed of safely ashore.