How big is my holding tank?

[basssears]

Tried to search the forums but didn't find anything, although I might have just missed it.

On new to use boat there is a holding tank under the v-berth... I think the tank itself is plastic encased in fiberglass but not sure (I'm not at the boat currently):


Regardless, the various listings / surveys etc all list the tank size differently (range from 6 gallons to 8 gallons to 15 gallons)... what's a safe (you know, none disgusting) way to figure out how big this tank is?

Thanks in advance,

Bass

[mbuckner]

Empty the tank, clean it out ... then start filling it with known gallons of water ... that should get you pretty close ...

Best regards,

Mike

[basssears]

So forgive my ignorance as I'm new to the holding tank thing, start filling it until "what"... ie what am I waiting for to happen so I know it's full... does something nasty start oozing out of the deck pumpout fitting, or how do I know it's full (no gauge or light on it)?

-- Bass

Originally Posted by mbuckner

Empty the tank, clean it out ... then start filling it with known gallons of water ... that should get you pretty close ...

Best regards,

Mike

[Calif.Ted]

Is that little box the tank ? measure the outside dimensions, 1 gallon water equals 231 cubic inches.

[wmcruiser]

Measure dimensions, google tank size calculator ,you can put in dimensions in and get gallons/litres of tank.

Sent from my HTC One S using Cruisers Sailing Forum mobile app

[mbuckner]

Use thet ank level gauge on your boat.

Mike

[basssears]

Don't have one. -- Bass

Originally Posted by mbuckner

Use thet ank level gauge on your boat.

Mike

[Stu Jackson]

I know high shcool math was always a bummer for some, but if you know the dimensions you can figure out the capacity.

How holding tanks work (scroll down and look at the diagrams):

Selecting a Sanitation System | West Marine

Good luck.

[StuM]

Originally Posted by Calif.Ted

Is that little box the tank ? measure the outside dimensions, 1 gallon water equals 231 cubic inches.

US or Imperial gallon?
I litre equals 1000 cubic centimeters.

[mbuckner]

Originally Posted by basssears

Don't have one. -- Bass

Since you are going to the effort of identifying the holding tank capacity, this would be a good time to install some type of level indicator to remove the tank level status question in the future.

Regards,

Mike

[Roy M]

So many hoses, it's hard to tell. First, empty the tank, any way you can. Then, locate where the vent hose exits outside. Then, fill the tank with measured volumes of water through the deck pump out fitting. Don't have one? Then pour measured volumes of water into the toilet and pump it into the holding tank until the water comes out the vent hose. The volume is slightly less than what you put into it (less the volume in the vent hose). Done.

[Calif.Ted]

Yep, US gallons and 4 pecks in a bushel still too.

[jeepbluetj]

Originally Posted by basssears

So forgive my ignorance as I'm new to the holding tank thing, start filling it until "what"... ie what am I waiting for to happen so I know it's full... does something nasty start oozing out of the deck pumpout fitting, or how do I know it's full (no gauge or light on it)?

-- Bass

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)

[boatpoker]

I'd be more concerned about what uric acid has done to those cheap domestic gate valves than the size of my tank.

[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.