Re: Graywater smells worse than Blackwater...
The reason is probably the fact that you put many types of grease into the gray tank which tend to coat things and most do not treat the gray water either. We actually do not treat black water as fulltimers, but we do at times address the gray. Grease when it becomes rancid will become very odoriferous in a fairly short time in hot weather. It is really quite normal and very common for it to smell worse than the black because the black has more natural tendency to break down.
I would never put bleach or such things into the waste tanks. While that will stop any odor for a short time, it does so by destroying all of the helpful bacteria that causes the contaminates in your tank to break down into liquids so that they will be easily emptied out. In addition, should you put a large enough amount to actually do much, it can also cause problems in septic systems which are very common in RV parks. With bleach it also depends upon the size of your waste tank just how much would be required to do anything, but even if it helps, the rancid residue will remain, it just won't smell for a while.
A much better approach is to use one of the bacterial products to treat your gray water with from time to time for that same purpose. We also use a mix of either dishwasher detergent or laundry detergent and water in our tanks just before travel a couple of times per year to remove any residue that has built up in them.
