I have a bath and a half in mine. I have 4-40 gallon tanks (160 gal total). Fresh water 47 gallons.
Black #1 is master bath and will last 5-6 days without rationing.
Gray #1 is shower and master bath sink and will normally last 3-4 days with the 3 of us. Oxygenics shower head at 2.5 gpm. Partner uses hot shower to help manage pain.
Gray#2 kitchen sink is 2 maybe 3 days max. The flow restrictor is removed from the kitchen sink because she wanted more flow to fill pots but leaves the water running while doing dishes. Since I normally have full hookups, I'd rather pull the drain valve than argue about water usage.
Black #2 is the half bath toilet ad sink it will last 7-10 days unless the grandkids are visiting then maybe 2-3 days (9 additional people)
If I don't have sewer, I have to dump every 3 days because of gray water.
Gray tanks fill up 1st as a rule. If my Gray #2 was a 60-80 gal I'd be happy. I could last 4-5 days then.
Many people who boondock I've read will wash dishes in a dish tub and dump it outside in a bush or down their toilet to extend gray tank capacity.
There are many techniques of tricks to make tanks last longer. All depends upon you and what you want to do. Also depends upon your partner(s) and their attitudes.