Min. black tank for 7 day Boondock?

figure an average of a half gallon per flush.

the black tank is not your issue - grey tank and fresh water - if you want to shower or wash dishes. There are ways around both, but I fill my grey or run out of fresh before I fill the black.

We had TC with a 25 gal black tank.
Family of 4, “most” #2s deposited in the camper toilet. Less than 50% of #1s in the camper. 1 week was about the practical limit. More than a week and you didn’t want to drive very far before dumping it!
2 people, 25 gal would comfortably go a week I’d say.

The recommendation to use plenty of water with flushes is valid, to a point. If parked long term it’s more critical. If camper is mobile, shaking things up does a good job without alot of “extra” water.

IMO, for boondocking fresh water capacity is the biggest priority by far. Black tank second, grey water 3rd. Bigger the better obviously. But despite some of the comments about how horrific it is to dump gray water in the woods, it can really be done very easily and cleanly and without scrutiny from those around with just a little common sense.

I know the replies will start flying over my last comment so let er rip, but if you were camped next to me you wouldn’t know I just dumped my gray water last night, so ya wouldn’t have anything to complain aboot! Lol

25 is plenty for two. If the campground has a toilet to use in the day then even easier.

OP...just too broad a question to answer. How private is the boondock? Are you willing to P, same place as your pet, or coyote, or bear? Even 25 gal black, may last two people a week.

My black is 40, my two grays equal 80, and my fresh is 66 gallons. As mentioned above, looking at my numbers, the fresh is going to be limitation.

Since many toy haulers boondock, it is common for them to have 100 gal fresh.

Jerry

Depends on your wife mainly. Some women use 1/2 roll of TP every time they are on the stool, thus having to flush several times to get it all down. My experience would say 25 gal. is enough for 3-4 days max.

In 50 years we have never filled our black but the grey fills up in several days.
Fresh can always be added....but then where is it going? Black or grey?

My Retro trailer has a 17 gal. black tank. DW and I can camp for 4 days easily without dumping. I would think 25 gal. could last us a week if we were careful.

I would think 25 gallon black tank would last a week, you will have to watch the gray tank. We went with a Outdoors RV because of the water tank 78 gallons, black 40 and gray 40. After camping for a week we can dump the tanks at our local treatment plant.

Unless you have explosive diarrhea a 25 gal black will be fine for 7 days. Even though we have a 40 gal black we could easily get by on 25. The nice thing about a larger black tank is it allows us to dump some grey sink water down it so our 40 gal grey won't fill as fast.

Me too. 25 gallons of black tank capacity is plenty for a couple boondocking for a week.