Back before I had the much-thirstier macerating toilet, I made a point to do the dish-tub trick, and to keep a bucket in the shower that captured part of the shower water and used that for flushes, etc. Now, the black fills at almost the same rate as the gray because the macerator toilet uses WAY more water per flush than the gravity toilets. If you have a gravity toilet (probably 98% + of Airstream/Argosy trailers?) it's definitely worth the effort for extended boondocking.
Zero Gravitas — 2017 Flying Cloud 26U | WBCCI# 15566
He has all of the virtues I dislike and none of the vices I admire. — Sir Winston Churchill