Black Water Tank Missing Capacity

[scoobybri]

We just bought a used 2015 Cruiser RV Fun Finder F233RBS. It is a 24 foot travel trailer and we love it. We have been RVing for awhile so I'm knowledgeable about tank maintenance on these types of RVs. On our first outing out, we had some odor problems in the bathroom. After a normal dump and chem treatment, we still had an issue the next time out. I checked the P-trap in the sink and the vent on the roof and everything was fine. So I decided to do a full black water tank soak for a few days with some Oxyclean to see if I could get any dried on solids that may have been stuck in there from the previous owners. The spec for the black water tank that I got from calling Cruiser is that the camper has a 38 gallon black water tank. So I measured 5 gallons into a bucket and began filling the tank 5 gallons at a time. By the time I got to 30 gallons, the tank was full! As in water was backed up into the toilet. I drained it after a few days and got no additional solids. Filled it again and got to 30 gallons when it was full. What gives? I can't believe that there are 8 gallons of dried waste in the tank. I guess it could be possible but it seems unlikely.

Any ideas?

[Bert_Ackerman]

Lantley wrote:
How much residual water remains in the tank? The tank does not drain to a bone dry status.

? My black and gray tanks always seem to drain to bone dry status taking into account the bottoms are sloped, and the nipple is formed into the tank so it's invert is even with the tank bottom. I can see a fresh tank holding residual water, but if it's the typical black or gray tank then something else is going on for it to hold enough water to affect overall capacity, like a big loogie jammed into the outlet or something.

[Lantley]

How much residual water remains in the tank? The tank does not drain to a bone dry status. THere is always some water left.
Where is the output pipe in relation to the tank? I doubt it is located in the very bottom of the tank.
Most likely it's attached to the side of the tank a couple of inches from the bottom. Hence the tank never drains completely and always contains some water.

[Bert_Ackerman]

wildtoad wrote:
I doubt anybody physically checks the actual holding capacity of the tanks when they are doing a PDI. When checking was your unit dead level? If it means that much to you get a flexible camera probe and take a look.

I always check the tanks for capacity, we once learned the hard way on a rig we ordered that came with different capacities than listed. All it takes is a garden hose and a $15 flow meter, 20 to 30 minutes. If the dealer wants to B&M about it for the the time it takes or anything else then he can pound salt and I'll purchase elsewhere.

It's not a big deal if you always have hookups. If you go rustic or boondock a few gallons less in capacity can be a big deal. It might be the difference on a given stay between toting Blueboys and/or jugs of water, or not.

[lane_hog]

I suspect you didn't get the stock tank. 8 gallons is a lot of space...

So is 30 gallons. The average adult "outputs" about 0.5 gallons per day, so a party of four adults would fill 30 gallons in about 10 to 14 days depending on how long people flush and use the sink.

[mobeewan]

If the tank vent pipe is installed too deep into the tank, it can stop by the tank from filling completely.

[wildtoad]

I doubt anybody physically checks the actual holding capacity of the tanks when they are doing a PDI. When checking was your unit dead level? If it means that much to you get a flexible camera probe and take a look.

[Bert_Ackerman]

Terryallan wrote:
I'm betting it is just a 30 gal tank, and it was mistakenly installed. the brochure claims 38 gal

Bill.Satellite wrote:
A number of people making "assumptions"! Why would a manufacturer lie to its customers?

Mistakenly installed, lies, and assumptions.

Here is an assumption. When the manufacturer is in the middle of a production run of the 275FLSD, and all of a sudden they realize that somebody over in procurement dropped the ball and did not order a sufficient number of 38 gallon tanks, they go a scrambling. They don't stop the line. They find some 30 gallon tanks obtained for the 17LPDC model that will fit, or they'll make them fit, and throw those in. They do the same with anything and everything be it a tank, an appliance, a sofa, anything.

Hence the disclaimer they all have on brochures and websites that state they can change materials and specifications at any time without notice.

If you order an RV at the dealer because it has some features you want, when it arrives you had better go over it with a fine tooth comb before signing on the line, because they very well could have changed one or more of the things you specifically ordered it for.

[RJsfishin]

It is what it is. Capacity calulated from dementions, and usable capacity from real life reality, can be 2 very different capacities. Its always been that way.

[Dave_H_M]

If it ain't broke why mess with it.

As Richard Rawlings says, let her rip tader chip. :W

[mchero]

Cut access panels, no need to "rip it out"

[scoobybri]

CapnCampn wrote:
Can you get to the outside of the tank to do some measurements? If so, you can calculate the approx. capacity. If you're getting less than that, it could be "stuff" or an air bubble like was mentioned.

CC

The bottom of the camper is completely insulated so I would need to tear it out to see the tank. I wish it was as easy as measuring the dimensions.

[scoobybri]

Bill.Satellite wrote:
If you shine a light down the toilet, do you see anything that looks like it's not the flat bottom of a tank?

I can see the bottom of the tank, I think. I see black plastic.

[ItsyRV]

Or, you're not actually emptying all the waste in the tank. There could be a small blockage built up at the valve "ScoobyBri Dam, the 174th wonder of the world" causing a reduction in new holding capacity.

[STBRetired]

Easiest way to make sure is to crawl under the trailer and look at what is marked on the side of the tank. Then you know for sure. I would guess that there is a "downpipe" where the toilet is mounted to the tank that extends a few inches into the tank. When water reaches the bottom of the pipe, you end up with an 8 gallon trapped air bubble.