Spec for black water tank is 34 gal yet 21 fills it???

Ed

Not always. My black water tank has the three inch pipe that runs about 5 feet, to a valve. Now when I start using the potty, the first fluids in, do nott magically set in the tank, but travel all the way to that valve. I would not think 5 gallons of water in that pipe would be too far from the mark. Now solids, those will pretty much set on the bottom of the tank, until the pipe is full, and the tank itself begins to fill.

I hadn't considered the volume of the piping as added space however it can't be considered as tank volume.

The top of the tank can also sag, taking up some of the volume. The old tank in my Jayco was sagged a good 2" in the middle.

eb145 wrote:
I crawled under my trailer and found the manufacturer's name and part numbers stamped on the grey and black tanks. They were identical tanks - same manufacturer and part numbers stamped on them. When I checked the tank manufacturers web site, the tanks were listed as 5 or 10 gallons less than the specs listed by the trailer manufacturer.

The trailer manufacturers seem to have fine print about "specs may change without notice"...

Ed

Not always. My black water tank has the three inch pipe that runs about 5 feet, to a valve. Now when I start using the potty, the first fluids in, do nott magically set in the tank, but travel all the way to that valve. I would not think 5 gallons of water in that pipe would be too far from the mark. Now solids, those will pretty much set on the bottom of the tank, until the pipe is full, and the tank itself begins to fill.

Mine are all stated 50 gallons. I made sure like another poster...used a 5 gallons bucket for water and filled all tanks. Mine all were 50 gallons.

I measured the tanks.

Fresh: 62.8 gallons. Advertised: 63 gallons

Black/grey 32.1* gallons. Advertised: 34 gallons. Manufacturer: 30

The black and grey calculations are prone to more error due to the odd shape. Those tanks are suspended by upper edges or horns that run the length and may be part of the usable volume. These tanks are also tapered. *I calculated the horns would hold 2.1 gallons if hollow if not then the tank is the 30 gallons as stated by Ameri-Kart. Which is probably the case since they made the tank.

So the first replies may be correct in that there is something inside consuming space. Back to the rinse. I also have a borescope and have used it for a household sewer pipe inspection.

Reg

Thanks you all for the feedback. More than likely the tank's volume is indeed less than advertised. With marketing the way it is it's too easy to lie - I mean accidentally post inaccurate specifications. Like someone mentioned funny how it errs in favor of sales.

I'm sure there could be some build up in the tank but 41%? Plus the RV is in such good shape it looks new. So probably little used.

I also struck the tank's bottom with the wand when washing down the insides. What I'll do is look for specs on the outside and not finding that attempt to measure the outside and do a little math.

Fortunenately it's just us two and we haven't had a shortage of ullage thus far.

Reg

I wondered about the same thing...how does one measure what comes out of a black tank?

YOU can measure it coming out, I measured it going in.
I was born, raised, and worked on a farm. If this is the worse
thing anyone does in their life, they've had a pretty good life.

Or what goes INTO it, for that matter...?

Empty tank.
Mark a 5gal bucket at the 4gal line. Less slop this way.
Get water hose.
Start filling and emptying bucket.
Count buckets.
When full, buckets x 4 = gallons in.



To OP: maybe cheap, disposable camera on a string but I don't know if they have an exposure timer on them.

I bought a truck camper that advertised 18 gal. black tanks. Could only get 14 gal. in it before it reached the top. Called the owner of the company and he went to the warehouse and started filling the tanks and he could only get 14 in them. He called the tank manufacture and set 'em straight and they came up with a new tank that was legit. They installed one free in my camper. If you can remember Cameo came out with the wrong specs and replaced a bunch of tanks on their fifth wheels. Funny how you never get one that holds more than it should.

Venting was mentioned along with burbling. ISTR in an RV fix-it book that the vent tube that goes to the roof can come away from the top of the tank and drop farther into the tank, so it cuts off venting when the tank gets that full.

Sorry, can't remember details or what you do next! :( Might have been in that Woodalls' book by ? Bill W something ? --several editions over the years. Got one out from the library a while back--lots of good info.

I crawled under my trailer and found the manufacturer's name and part numbers stamped on the grey and black tanks. They were identical tanks - same manufacturer and part numbers stamped on them. When I checked the tank manufacturers web site, the tanks were listed as 5 or 10 gallons less than the specs listed by the trailer manufacturer.

The trailer manufacturers seem to have fine print about "specs may change without notice"...

Ed