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Old 17-07-2019, 12:13   #1
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Holding tank questions

On our boat the holding tank is very easy to access (behind a panel in the head which is designed to be opened) and it is plastic. The tank is only 20 gallons which has me concerned.


With just the two of us, if we decide to anchor out for a few days, how soon will the tank get to the point it must be pumped out? (I know there are several variables, just trying to get ball park time.)


For that matter, can you let a holding tank get completely full before pumping (full, not overflowing), or is there a % full at which point it should be pumped out? The distance to a pump out station does influence that decision.



The tank is plastic and I think I could see the level of waste in the tank. Are there any devices I could hold up to the tank and find the level? I guess rapping on it might determine the level, but I'm not certain how well I could detect the difference in sound.
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Old 17-07-2019, 13:22   #2
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Re: Holding tank questions

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Originally Posted by Dr. D View Post


With just the two of us, if we decide to anchor out for a few days, how soon will the tank get to the point it must be pumped out? (I know there are several variables, just trying to get ball park time.)
5-9 days

when we know we are going to be able to pump out in a few days we use more flush water to reduce scaling

when we know we wouldn't be able to pump out for a while we use less, but this results in more scaling and I have to clean flush more often
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Old 17-07-2019, 14:18   #3
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Re: Holding tank questions

My Vacuflush holding tank has level sensors, Empty, ľ, Ĺ and Full, that are handy.

A bright flashlight aimed at the side of the white translucent tank reveals the visual level.

The interior of my empty tank is periodically manually scrubbed clean to aid the visual inspection and to keep things working good.

On mine, I never go full because even a small amount of liquid in the charcoal vent filter destroys that part.
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Old 17-07-2019, 14:38   #4
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Re: Holding tank questions

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Originally Posted by Dr. D View Post
On our boat the holding tank is very easy to access (behind a panel in the head which is designed to be opened) and it is plastic. The tank is only 20 gallons which has me concerned.


With just the two of us, if we decide to anchor out for a few days, how soon will the tank get to the point it must be pumped out? (I know there are several variables, just trying to get ball park time.)

I find that it is ordinarily 1-2 gallons per person per day depending on how much water is used per flush.



Quote:

For that matter, can you let a holding tank get completely full before pumping (full, not overflowing), or is there a % full at which point it should be pumped out? The distance to a pump out station does influence that decision.

It depends on the design and condition of the vent piping and, in some cases, angle of heel and sea state. If the vent hose exits the tank at the top you can use nearly 100% of the capacity. Sometimes there are design constraints that lead to side vents, which reduce the usable capacity somewhat (10-20%).


Quote:
The tank is plastic and I think I could see the level of waste in the tank. Are there any devices I could hold up to the tank and find the level? I guess rapping on it might determine the level, but I'm not certain how well I could detect the difference in sound.

Flashlight sometimes works depending on the tank material and condition (cleanliness). There are sensors you can buy. None of them are reliable over the long run, but the ultrasonic ones are the least bad.
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Old 17-07-2019, 19:18   #5
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Re: Holding tank questions

I can give "ballpark" math: The average adult uses the toilet 5x/24 hours...average flush volume from most toilets is .6 gal. So on average, 2 adults will put 6 gal/day into the tank. So, on average, a 20 gal tank should last 2 adults at least 3 days.

There are ways to improve on that... If you have a manual toilet, use the dry mode to flush urine only most of the time, switching to "flush" only once or twice a day to rinse the discharge line. If yours is an electric toilet that can only be flushed bringing water in as bowl contents are pushed out, you may have to use the lee rail (although your wife may not consider that an option, you can) when you're not likely to run afoul of any indecent exposure laws. Or go swimming if you can. ALWAYS add water to the bowl ahead of solid waste...if your toilet isn't one that can bring flush water in and hold it, use a cup from the sink. This will greatly reduce the amount of flushing needed to leave you with a clean bowl and discharge hose. Learn to use a lot less TP than most people typically use at home. Doing all the above should give you another 2 days. I'm guessing that Reston VA is your home, but not where you keep the boat. If it's anywhere near the mouth of the Bay, it may not be that hard to get 3 miles offshore from Hampton VA to dump the tank in a pinch. If it's further up the Bay, that's prob'ly not a viable option.

Yes, you can fill the tank to capacity, but 3/4 full is a safe "target" amount. I'd strongly recommend that you install a tank level monitor. The SCAD "solo" is reasonably priced and easy to install, plus it has the added advantage of a sender that attaches to the outside of the tank instead of an internal sender that may require drilling a hole in the top of the tank. Scad Tank Monitors

You're welcome to give me a shout directly if you have more questions about your sanitation system...I'm always happy to help.
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Old 17-07-2019, 19:43   #6
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Re: Holding tank questions

Yep. We found out the hard way how fast they fill up. The tank inspection lid can have a rubber seal that is hard and leaks a bit. If you over fill the tank it can leak out of the top and create a mess (dont let that happen while at anchor!) Even if you fill it all the way and its an old seal it can still seep out.

I use a flashlight and check the holding tank as described above daily.

Urine fills a holding tank up fast. Find ways as mentioned above to remediate that. While we have a Y valve to send overboard if 3 miles out, we don't have a macerator so it’s a bit of a concern for us with a 16 gal tank. My wife and I can stretch it out to about 4 days max. I really considered a composting toilet, but there is no way it can fit.

The holding tank is the one thing on my boat that forces us off the anchor and back to a marina. I’d love to find ways to stretch it.
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Old 18-07-2019, 10:43   #7
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Re: Holding tank questions

Thanks for the input. Gosh, I wish the tank was larger....
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Old 18-07-2019, 11:55   #8
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Re: Holding tank questions

If the Bay is your primary cruising grounds, there may be an even better option: a USCG certified treatment device that makes it possible to flush overboard instead of into a tank in all waters except those designated "no discharge"...the Chesapeake Bay is NOT a NDZ (no discharge zone)...the discharge of treated waste is legal everywhere on it except for one small harbor--Herring Bay (and a couple of well intentioned but misguided marinas). Check out the Raritan PuraSan Raritan PuraSan Promo Sheet

--Peggie
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Old 18-07-2019, 12:15   #9
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Holding tank questions

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Originally Posted by peghall View Post
I can give "ballpark" math: The average adult uses the toilet 5x/24 hours...average flush volume from most toilets is .6 gal. So on average, 2 adults will put 6 gal/day into the tank. So, on average, a 20 gal tank should last 2 adults at least 3 days.

Iím glad to see that, our 35 gl tank wonít quite make it a full week, and I thought we were just really wasteful, as I see often how people act as if we should get at least two weeks, and thatís not happening, no way.

Had me wondering how and why we used so much more water than everyone else, now Iím thinking maybe we donít.
Maybe a 35 gl tank is only good for two adults just shy of a week.
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Old 18-07-2019, 12:32   #10
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Holding tank questions

a64, our tank is also 35 gallons and with two of us onboard we also get just shy of a week with our VacuFlush using freshwater. Where we sail on the west coast it can be difficult to find a convenient and working pump out but it isnít too hard to go offshore far enough to manually discharge.
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Old 18-07-2019, 13:02   #11
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Re: Holding tank questions

Thank you, that answered another question of mine, that was would a vacuflush cut way black on consumption? I guess it wouldnít, thanks
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Old 18-07-2019, 14:52   #12
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Re: Holding tank questions

Based on Peggieís advice we use plenty of water for each flush. We could perhaps use less water for urine only flushed and thereby not fill the holding tank as quickly but using enough water to completely clear the pipes keeps the system running well. It is easier to pump out the holding tank that to change duckbill valves.
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Old 18-07-2019, 17:03   #13
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Re: Holding tank questions

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Thank you, that answered another question of mine, that was would a vacuflush cut way black on consumption? I guess it wouldnít, thanks
My Vacuflush usage is to hold the flush pedal down, then count to five when doing number one and hold it down until I hear the vacuum pump through the plumbing when doing number two.

This method has been working well for me.

There are techniques that would consume less fresh water / fill the tank less, but my PRIMARY concern is to avoid joining the Platypus Club by ever having to fiddle w/ duckbill / Joker valves on a failed system.
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