How big is my holding tank?

[UNCIVILIZED]

If it's easy to take off of the boat, then do so, fill it with water, & seal it.

Then completely fill something a lot bigger, or fill something bigger up to a witness mark.

Then insert the filled tank into the bigger tank, allowing it to overflow, or the water to rise above your initial witness mark. And if the latter, then make a 2nd witness mark.

Now, lift out the tank, & pour water back into the bigger tank until it's full/it reaches your 2nd witness mark... & poof, you know how big the tank is.


Or, as it's been stated in other terms, 1 gal.= 1/8 cubic foot.

[Xthewater]

Originally Posted by jeepbluetj

Something nasty will come out the vent if it's lower than the pumpout. The pumpout if the vent is higher and the pumpout is open.

I'd use some basic geometry and math.

If the tank shape is so irregular, you can fill it from the pumpout (with water) and see the level rise.

But so what? Let say you figure out that you have a 40 liter tank. (~10.5 US gallons, 8.8 imperial gallons, something like 1.2 US bushels) But now what? Do you know the volume used every time you/guests take a leak? Flush? Etc? Sure it's nice to be able to tell folks you have a 4.54 peck holding tank, but it doesn't tell you when it's gonna be full. But if you know that you pee a cup each time, and use 2 cups of flush water that 40 liter tank will be full in 55 pees. I propose a new unit of volume named a "Pee" that's equal to 3 cups.

Either:
1. Live with it for awhile, you'll figure it out.
2. Put in a gauge.

(units chosen to maximize humor value. Sorry, couldn't help it)

Almost peed myself reading this! Might need a poop volume component in the calculations, perhaps an average calculated as a ratio. Which would make this a unit of volume named a "poopee?"

[seasick]

I second boatpoker's observation. Those gate valves were my first concern. Volume of tank in gallons is less important than number of average head uses per pump out.

[Sailorbob8599]

Originally Posted by Roy M

boatpoker, I only saw a plastic diverter valve in the photo, which is unlike a cheap domestic gate valve. Did I miss something? Otherwise, there appears to be no issue with basssears' holding tank.

Look again in the top R.H. of the photo, you'll see the round cast metal handles of the 'cheap' gate valves referred to ... and yes, they surely are cheap valves, intended for residential use ... NOT a marine application. But then, maybe that is all the owner can afford and is willing to trake the risk.

[Stu Jackson]

Peggie Hall, who wrote the book on marine heads & boat odors, notes that 3 gal/person/day is a reasonable figure for estimating purposes.

[Redline452]

I see gate valves on two through-hulls, which is NOT a good idea - they fail in ways that prevent closing completely. Not his original question, but if it was my boat, I'd change them at next haul-out (or schedule one to do so ).

[redsky49]

There appear to be several thru-hull fittings in the pic - one Marelon or similar plastic valve, and a couple of what appear to be gate valves.

These gate valves, based on the multi-colored handles, appear to be from the Red-White Valve Co. If I am correct in this they will have a little tab in the center of the handle indicating so, as well as the country of manufacture (likely Japan, but not necessarily so).

These were marketed for residential and commercial use, typically submitted by cost-conscious Contractors, and were not especially high quality. In any case, they are definitely not indicated for marine use, especially as thru-hull fittings.

The mix of both plastic and brass/bronze fittings would concern me. I wonder if there is a bonding system on this boat?

I would also look at the backing plates for these fittings.

Don't mean to alarm the OP, but this might all be something new for him/her, and Knowledge is power, right?.

[boatpoker]

Two gate valves circled.

[redsky49]

And to rain further on this parade, the corrugated hose that appears to be used for both the inlet and outlet lines for the holding tank really should be changed out for smooth bore hose, designed specifically for sanitation use. The grey stuff shown is not sanitation suited, and you will curse this stuff further down the road.

Just my opinion.

[Calif.Ted]

The OP has another thread regarding the thru hulls and I believe he has decided to replace.

[neophytecruiser]

From the photo, the holding tank looks to be rectangular. Easy enough to measure the volume in cubic inches (length x width x height) and then, as others have suggested, covert this volume (e.g., cubic inches) measurement to gallons (multiply your cubic inch volume by 0.004329 to convert to U.S. gallons).

[redsky49]

I should also add that corrugated hose is quite difficult to properly clamp. From the pics, you can see that someone has slathered some kind of sealant all over the connections to the Y-valve. Apparently, these connections have leaked and someone kludged together a "fix".

[basssears]

Just to paint the complete picture, this is a new to us boat with some projects (although not too many) for sure.

In fact, the holding tank size is only somewhat tangential to major project #1, which is to replace all the through hull fittings and then use proper sea valves on them... it is (as best we and a surveyor can tell) the only major safety issue this boat has.

Only real reason for investigating size of the holding tank right now is that we would be replacing all the hoses (for reasons noted already, i.e. not proper sanitation hose, they stink, and the hose clamps don't seal them tightly) as soon as the new through hulls are in, but if the tank is really tiny we might blow off the whole thing, cap off the through hulls and go to dessicating toilet like C-Head/Nature's Head/Air Head.

-- Bass

Originally Posted by Calif.Ted

The OP has another thread regarding the thru hulls and I believe he has decided to replace.

[redsky49]

Originally Posted by basssears

Just to paint the complete picture, this is a new to us boat with some projects (although not too many) for sure.

In fact, the holding tank size is only somewhat tangential to major project #1, which is to replace all the through hull fittings and then use proper sea valves on them... it is (as best we and a surveyor can tell) the only major safety issue this boat has.

Only real reason for investigating size of the holding tank right now is that we would be replacing all the hoses (for reasons noted already, i.e. not proper sanitation hose, they stink, and the hose clamps don't seal them tightly) as soon as the new through hulls are in, but if the tank is really tiny we might blow off the whole thing, cap off the through hulls and go to dessicating toilet like C-Head/Nature's Head/Air Head.

-- Bass

Congrats on the new boat.

My feeling is it takes a couple of years to really know a new boat, so you will likely have some questions further down the road.

Feel free to post any other questions. We're from the Internet. We're here to help. We can criticize anything.


Good luck!

[Dave22q]

Not sure why you care but an easy step is arrange for a pump out. After they finish, add water through the pump out port measuring the quantity as you go. Stop when full (you will see water level, some may come out on deck). Repeat pump out. If you round the quantity down you have a good estimate of your holding tank capacity. Quickest way is just time how long to fill with the water turned fully on. Then measure the approximate fill rate by timing the fill on a known container.