I've always been concerned about that issue, and it is a real one.
It's not often mentioned, but it should be addressed.
The first thing would to be to understand one's digestive system, and plan one's food consumption based upon the biologically normal functions.
If your bowel has a tendency to become active mid-morning, then don't consume anything that would generate an inordinate amount of waste. And likewise, between dives, don't consume anything which you know activates your bowel.
Timing is everything. I think each of us knows our daily routine. Just keep that in the back of your mind when planning your trip and adjust your meal schedules and menu accordingly.
Now, IF one were to soil one's wet/dry suit, I would assume that the diver would refrain from doffing it while on board the boat. Shore dives could be a different matter because of the immediate, for the most part, availability of more private quarters.
The heads on most boats don't give sufficient space to handle such a situation in order to clean up.
Now if the water temperature was permissible, I suppose one could, after doffing the gear, hop back into the water, swim to the bow where there's a bit of privacy, partially doff the wet suit and attempt a good rinsing.
So, if it happend to me, I guess I'd live with the mess until such time I could get to a convenient place to clean up.
If it were my wet suit I'd throw it away and buy a new one (I buy inexpensive wet suits).
If it were my dry suit, I'd just sit down and cry, then take it to the freakin car wash.
the K-lean it REAL GOOD ! ! !