coat your hands with cold bacon grease... now put a generous amount of dish soap on them... run cold water over your hands. How much water did it take to get your hands clean? Probably quite a bit of water and you needed a paper towel to really wipe it off. Rinsing alone is kinda endless.
coat your hands with cold bacon grease again... now put some distilled vinegar to them. A TBSP at a time. Now rinse your hands with cold water.
Did one work better than the other? I would tend to think the distilled vinegar would be a good de-greaser... at least better than dish soap.
Don't use cheap dish soap.
Don't put crud, like grease down into your gray tank.
If you have to... dump your pan of greasy dish water down into the black tank (where you can hose it out) rather than in the gray tank where you can't do much to flush it out.
Now, go buy 10 gallons of CLEANING (5% acidity) distilled vinegar... pour it into your gray tank and go for a drive. Don't worry about rinsing it out.
JMHO