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Old 09-17-2018, 10:14 PM   #1
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Holding tank math

I have a tank level monitor but it is seriously lacking. I will get and install a different type of system at some point, Peggie has mentioned a good one. In the mean time, I am still looking at a way to tell how full or empty the holding tank is so there aren’t any unpleasant surprises. I finally came up with a solution I hope will work. Math.

My tank is 50 gallon or 189 liters. I figure that the average adult produces 3 liters of waste per day. I have a Tecma Silence head. It has two buttons. The first is a pre-flush which puts .5 liters of water in the bowl. The second is the flush button and the head uses .75 liters to flush. The idea is that for solid waste you use the pre-flush button before, and the flush button afterwards.

So my idea is this, simply count the number of times the flush button is pushed. I don’t care which button is pushed, just count each button as it is pushed. So I figure that I will consider 200 pushes until I need to empty the holding tank. Given the enormous size of my prostate and the tiny size of my wife’s bladder, we should be hitting a button 200 times in a week. 200 flushes would be roughly 145 liters (remember the pre-flush is only .5 liters). 7 days would be 42 liters of waste between the two of us. So that would make 187 liters in the holding tank.

So my plan is simply to use a tally counter with the instruction to anyone on the boat to simply click it for each button push. If the counter says 175, then I will figure that the tank is 3/4 full and I can plan accordingly.

Time will tell if this works.
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Old 09-17-2018, 10:24 PM   #2
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Old 09-17-2018, 10:39 PM   #3
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Let us know how that system works out for you...
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Old 09-18-2018, 12:42 AM   #4
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You'll hopefully be flushed with success
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Old 09-18-2018, 12:53 AM   #5
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Did you allow for a bout of bad oysters that could blow out your math's and just about every thing else .
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Old 09-18-2018, 02:01 AM   #6
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Why not to use a digital counter like the Omron H7E serie, these are quite cheap and if you connect it to you switch you won't have to ask to people to push the counter button.

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Old 09-18-2018, 02:15 AM   #7
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Have you fitted an overflow receiver?
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Old 09-18-2018, 02:42 AM   #8
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What about a set of scales at the dunny door weigh in weight out. LOL



Better still HEHEH





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Old 09-18-2018, 07:21 AM   #9
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I prefer to visually check my holding tank level. No sensors to fail. You should be able to determine through routine, when your tank is a third to half full and then just start keeping closer tabs. The other considerations would be to plan more frequent emptyings and remove the anxiety. Considering how unpleasant an over fill could be, counting cycles on a variable volume adding system seems like an invitation for disaster.

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Old 09-18-2018, 07:39 AM   #10
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Originally Posted by Lou_tribal View Post
Why not to use a digital counter like the Omron H7E serie,
My thought, too.


I have the same concerns as others about the possibility of a failure when you are relying solely on the math, but I suppose if you are extremely conservative in your calculations it should be a reasonable way to at least warn you that you need to start being alert.


That said, an electronic circuit that would automatically keep track of how many times the button is pushed would be simple and cheap. Then you could connect it to an idiot light somewhere that would notify you that it's time to go and check it visually, or whatever.


Interesting idea, anyway.
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Old 09-18-2018, 07:50 AM   #11
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1/2 a million dollar boat why not just fix it now and stop stuffing around ??
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Old 09-18-2018, 08:30 AM   #12
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Originally Posted by dhays View Post
I have a tank level monitor but it is seriously lacking. I will get and install a different type of system at some point, Peggie has mentioned a good one. In the mean time, I am still looking at a way to tell how full or empty the holding tank is so there aren’t any unpleasant surprises. I finally came up with a solution I hope will work. Math.

My tank is 50 gallon or 189 liters.

FWIW... if the tank is labeled to hold 50 gallons... it might not. If you do the measurements taking the location of innies and outies into account, sidewall thickness, etc... you may find the true capacity isn't what the label says. (Ask me how I know that. OK, it's because our "40" gallon tank holds about 26 gallons.)

We've not had all that much difficulty with our gauge, once that true capacity became evident AND once we filled the tank to real capacity with a garden hose (put Mk I eyeball on the true tank level) and then looked at the gauge reading. (Ask me how I know. OK, when our gauge reads 2/3rds full, it's full!)

FWIW, our gauges use WEMA in-tank float sensors, relatively OK. Occasionally the float gets stuck with uric acid crystalline build-up, but that's easily cleaned with something like muriatic acid. We actually have two sensors now, so I can do a quick change and clean up the "old" one at my leisure. (Ask me... well, anyway... if our gauge doesn't start showing at least something within a reasonable period of time, I get suspicious, can swap sensors quickly if necessary. This part might be related to your math approach, although no real calculations involved; if the gauge isn't registering any activity within 3 days, I'm on the alert.)

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Old 09-18-2018, 09:11 AM   #13
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Why not just install a tank level indicator? The Profile system Profile Tank Monitors (also sold by SCAD Technology under their private label brand name for a higher price Scad Tank Monitors than you can buy it direct from the mfr) is the top rated system and provides a 1/4, 1/2, 3/4 and FULL read out. Their "solo" (single tank) version is inexpensive and uses senders that attach to the outside the tank, so they never come in contact with the contents and therefore can never become clogged.



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Old 09-18-2018, 09:26 AM   #14
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Why not just install a tank level indicator? The Profile system Profile Tank Monitors (also sold by SCAD Technology under their private label brand name for a higher price Scad Tank Monitors than you can buy it direct from the mfr) is the top rated system and provides a 1/4, 1/2, 3/4 and FULL read out. Their "solo" (single tank) version is inexpensive and uses senders that attach to the outside the tank, so they never come in contact with the contents and therefore can never become clogged.

Yup. That is my plan eventually based on your prior recommendations. It is on the long list of projects to be done. In the mean time, I’ll see how this goes.
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Old 09-18-2018, 09:45 AM   #15
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Quote:
Originally Posted by gaston View Post
Did you allow for a bout of bad oysters that could blow out your math's and just about every thing else .

There is some built in leeway for this eventuality. The pre-flush is only .5 L yet is getting counted as .75 L. So in the event of a negative gastrointestinal event, it is possible that the allow 3 liters of waste/person/day may be exceeded, but the 200 count will be reached sooner and with more lower volume button counts.

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FWIW... if the tank is labeled to hold 50 gallons... it might not. If you do the measurements taking the location of innies and outies into account, sidewall thickness, etc... you may find the true capacity isn't what the label says. (Ask me how I know that. OK, it's because our "40" gallon tank holds about 26 gallons.)

Good point. The other issue is that with a pump-out, the tank doesn’t really get completely emptied. Hence I may modify my count number to provide a little more headroom in the tank (see what I did there?).

The level sensors in the tank actually work pretty well. I’ve only removed and clean them once and it wasn’t actually needed. The problem is in the lack of information they provide. Three floats that tell me “Low”, “Mid”, and “Full”. The Profile system would give a much more useful 1/4, 1/2, 3/4, full.

Quote:
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1/2 a million dollar boat why not just fix it now and stop stuffing around ??

In my case, less than 1/3 million, but your point is a good one. This will be a stop-gap measure until I can put in a different tank level system.

Quote:
Originally Posted by Lou_tribal View Post
Why not to use a digital counter like the Omron H7E serie, these are quite cheap and if you connect it to you switch you won't have to ask to people to push the counter button.

I thought about it and that is always an option if I find this system works well. A mechanical tally counter however costs $3 and no installation.
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Old 09-18-2018, 10:43 AM   #16
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I have a fool proof monitor. My tank is poly. It is mounted so I can see the top half of it and I marked it with level indicators on a strip of masking tape. I also put a light behind the tank. So to get the level I open the cabinet door and turn the light on - instant tank level determination.
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Old 09-18-2018, 10:56 AM   #17
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I have a fool proof monitor. My tank is poly. It is mounted so I can see the top half of it and I marked it with level indicators on a strip of masking tape. I also put a light behind the tank. So to get the level I open the cabinet door and turn the light on - instant tank level determination.
You can not go wrong with a light behind a poly tank. One look and you see exactly how full the tank is. This is how I have mine setup also.
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Old 09-18-2018, 11:54 AM   #18
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The level sensors in the tank actually work pretty well. I’ve only removed and clean them once and it wasn’t actually needed. The problem is in the lack of information they provide. Three floats that tell me “Low”, “Mid”, and “Full”. The Profile system would give a much more useful 1/4, 1/2, 3/4, full.

I saw what you did there!

Even Low/Mid/Full can be reasonably useful if you compare that to eyes-on tank levels. You might find that Mid is tolerable, and the minute the lights switch to Full you'd best be pumping out. Or that Full still leaves you a few days leeway, etc. It's the ground-truth comparison that begins to fill in some of the blanks.

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Old 09-18-2018, 12:01 PM   #19
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Originally Posted by HeadMistress View Post
Why not just install a tank level indicator? The Profile system Profile Tank Monitors (also sold by SCAD Technology under their private label brand name for a higher price Scad Tank Monitors than you can buy it direct from the mfr) is the top rated system and provides a 1/4, 1/2, 3/4 and FULL read out. Their "solo" (single tank) version is inexpensive and uses senders that attach to the outside the tank, so they never come in contact with the contents and therefore can never become clogged.



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I installed two of these...fresh water and holding tanks. Inexpensive, easy to install, great support from Dennis and no problems since the installation 7 years ago.
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Old 09-18-2018, 12:02 PM   #20
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Even Low/Mid/Full can be reasonably useful if you compare that to eyes-on tank levels. You might find that Mid is tolerable, and the minute the lights switch to Full you'd best be pumping out. Or that Full still leaves you a few days leeway, etc. It's the ground-truth comparison that begins to fill in some of the blanks.

Yeah, the problem is that when it says "Full" it really is full and you had better not flush the head. I've tried adjusting the level of the tank floats and that helps some, but not much. As it is now, as soon as the level shows "Mid" we are looking for a pumpout and yet there still is a lot of room in the tank.
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