We have a short list of sub 28' "couples" trailers that we are considering. Some have black tanks as small as 25 gal. What is a min. tank size, for a couple, that would allow us to boondock at least a week and not have to "blue boy" it?

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

Min. black tank for 7 day Boondock? | Good Sam Community

Huntindog
Explorer
Feb 05, 2022
First.. Most RVs listed capacity is not accurate.
They usually fall short of the stated capacity.
One of the first things I do with a new RV is to actually measure it, and log just how many gallons are in the tank for each light on the monitor. Then I can tell just how we are doing when camping. I have had 3 new RVs. My present one is the only one that held as much as the specs stated... My Momentum has very large tanks, and actually holds more than stated. With this one I no longer have tank anxiety. We recently were on a 3 week boondock hunting trip, and could have gone longer. Had FW to spare, and room in all tanks. I think we can do 4 weeks now.
On my previous RVs, Black was always the limiting factor... Getting more Fresh is easy. Getting rid of grey is as well.

My advice to the OP? since you are asking about boondocking, get the biggest tanks you can... And Grand Design seems to have good sized tanks that actually hold what they are supposed to.
ktmrfs
Explorer II
Feb 04, 2022
Our trailer has a 35 gallon black and two 35 gallon grey tanks. we often camp for a week with the two of us, two grandkids, and daughter and son in law. Have yet to fill up the black tank, and can make it on the two grey tanks if we are careful. Quick showers, paper plates etc. careful with water when dish washing.

Now another couple that camps with us with similar tank capacity couple with one kid, ends up needing to trudge off to the dump station every couple of days with the full blue boy from the black tank.

So........ answer is "it depends"
Lwiddis
Explorer II
Feb 04, 2022
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."

Some women? Oh my goodness!
Lwiddis
Explorer II
Feb 04, 2022
Me too. 25 gallons of black tank capacity is plenty for a couple boondocking for a week.
goducks10
Explorer
Feb 04, 2022
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.
Old_Days
Explorer II
Feb 04, 2022
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.
punomatic
Explorer
Feb 04, 2022
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.
IDman
Explorer
Feb 04, 2022
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?
MFL
Nomad II
Feb 04, 2022
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
time2roll
Nomad
Feb 04, 2022
25 is plenty for two. If the campground has a toilet to use in the day then even easier.

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Min. black tank for 7 day Boondock?

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