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Old 07-04-2013, 13:04   #1
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Holding tank size-is mine large enough?

Hello All

Just got done emptying our waste tank, and now it sits in the back yard, as we are trying to clean it before reinstalling it. What a job!!! This tank is original equipment...11 gals., 10 usable, installed in our 08 Larson Cabrio 260. We have a Dometic vacuflush head. All grey water is plumbed overboard.

Originally, I planned on changing the tank to a larger tank as it seemed last season we were pumping out just about every weekend(two days usage). As far as usage goes, I use the marina head almost exclusively, while my wife uses the head on the boat almost exclusively. We think that we are pumping out too often, and blamed it on the tank size at first, but I am wondering if we are not pumping out properly....I pumped the tank out at the end of the season(or thought I did) in anticipation of the winter. We spent extra time there to make sure we got everything, but I found this spring that we left the tank about half full!! Thank god it didn't burst over the winter!!!

Anyhow, since we were unsuccessful at the end of the season, I am wondering if we were not pumping the tank completely during the season as well, therefore possibly explaining the short cycles, if you will. This was our first year with this type of boat(cruiser), and much of the equipment. The tank is a poly tank, but stained on the inside to not allow us to see the level so well. There is not a level meter other than warning and full float switches and lights.

After reading some articles here, I wonder if my vent filter was clogged, or something like that. We bought the boat used from a local dealer. Could the tank have been so filled with sludge, that that never came out? The gray water was originally plumbed to empty into the tanks as well.....I replumbed that last year, but the fitting at the tank was loose(and had been by virtue of the caulk buildup). Anyone have any suggestions or comments? How much waste does one human make per day? I read here someplace that it is an average of 6 liters (1.59 gals) per day, which should equate to us being able to go longer than we have. I can fit a slightly larger tank, but would just as soon not if I don't have to...

BTW, I boat on an inland lake in North America, so there is no option of pumping overboard.

Thanks in advance.


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Old 07-04-2013, 13:09   #2
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Re: Holding tank size-is mine large enough?

Vent filters are NOT helpful, because they get clogged. A clogged vent will preclude you from emptying the tank.

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Old 07-04-2013, 14:04   #3
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Re: Holding tank size-is mine large enough?

The rate at which it fills in more a function of how thoroughly you flush. If for no other reason than to avoid the tendency to flush in sufficiently, you might want to replace it with a larger one. Ten gallon tank is not what I would consider adequate even for 2 people and with guests, ...
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Old 07-04-2013, 15:31   #4
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Re: Holding tank size-is mine large enough?

We found we used about 15 litres (about 4 gallons) a day with conservative use.

In the marina and with "emergency" use only it comes to less than half that. Does mean a morning run to the marina washroom though.

We have a 150 litre (40gal) holding tank so can get up to 10 days, but I'm usually checking pretty carefully after a week!

I find that 150 litres is about the minimum we're comfortable with. Even being right next to the pumpout it can be difficult to get the tank emptied if there is bad weather or the operator can get sick or the pumpout may not work or there may be limited capacity.

It sounds like you get a lot of use from your boat so putting in a much larger tank may be worth the considerable expense, time and disruption.
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Old 07-04-2013, 15:47   #5
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Re: Holding tank size-is mine large enough?

Another option.

If you have the space, get rid of the tank altogether and go with a composting head.
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Old 07-04-2013, 15:57   #6
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Re: Holding tank size-is mine large enough?

That's a small tank by my standards, but it depends on how you use it. We sail the Great Lakes so also must hold. Our old boat had 32 gallons, which was barely acceptable. Our current boat has a 25 gal. tank, which is too small for our usage patterns.

Regarding the quality of your pump out, perhaps you're not building up enough pressure to get everything. That might be a failing of the pump/service you're using. Or perhaps you're not getting a good seal at your outlet.

Make sure you flush additional lake water through the system once you figure you've evacuated it all. This cleans things out, and may dislodge any stubborn bits.

Finally, to ensure we get everything out I cover the vent (with my finger) so the tank can build up additional vacuum pressure. Be care when doing this, as you don't want to implode your tank. But it helps to get that final drop.
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Old 08-04-2013, 04:54   #7
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Re: Holding tank size-is mine large enough?

Some random thoughts:

If you've got the tank out now... and if a larger tank will fit... now's a good time to change it.

You can maybe use an air compressor to check that your vent line is clear (remove filter first, if you have one). Perhaps augmented by high-pressure water, if the vent line is constricted with sludge too.

Or... maybe now's a good time to change your vent line as well, if both ends are semi-easily accessible.

Vent filters can clog (as mentioned), but if you do your part (pump out appropriately) it's usually not a problem.

A vent filter may not be necessary on your installation, even if you have one installed. Park yourself near the vent outlet, have some one flush... and if it knocks you overboard, your marina neighbors will likely appreciate you having one. Otherwise, maybe you can do without.

I agree with the assessment that the pump-out service(s) you've used may be at least partially complicit.

It's not all that difficult to add a sensor system, especially since you have the tank out now anyway. Some systems use an internal float with an external gauge (e.g., WEMA) and some use en external strip along the outside of the tank (I forget brand names).

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Old 08-04-2013, 18:20   #8
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Re: Holding tank size-is mine large enough?

Thanks for all the replies..I just ordered a 31 gal holding tank and a 31 gal water tank(old water tank was only 18 gallons)!!!
Had thought that I was going to do this before.......wanted to save the cash...oh well. Will take the advice of as long as I have gone this far, might as well put it back together right.....or at least with bigger tanks. Thanks again all.

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Old 15-04-2013, 05:00   #9
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Re: Holding tank size-is mine large enough?

If you are worried about your vent being plugged get a tank emergency vent from Sealand. I watched by holding tank on my last boat collapse during pump out as my vent was clogged. The Sealand vent is just a backup and only opens if a vacuum develops in the tank that would crush the tank.
I have a Vacuflush toilet that uses less than 1/2litre of water per flush and a 45 gal holding tank. we use the rule 'if it is yellow let it mellow, if it is brown flush it down' and we get a couple of weeks before pumpout for my wife and myself
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Old 15-04-2013, 14:10   #10
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Re: Holding tank size-is mine large enough?

Thanks steveO, I just received my new 31 gallon tanks from Trionic corp and the waste tank comes with a vent for that purpose!! I am also in the process of building my own refillable vent filter......haven't tested the old one.....not sure if it is that important!! I think the new tanks will be good improvements...we use the boat as much as we can, and this should mean we won't have to travel to the pumpout station as much as last year!! Now I need to figure out how to mount mt hot water tank on top of the water tank without crushing it. Thanks for all the replies!!

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Old 15-04-2013, 14:17   #11
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Re: Holding tank size-is mine large enough?

I've got two 25 gallon tanks for a total of 50 gallons. Wouldn't want less.

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