Holding Tank Capacity

[tonywright]

Has anyone else measured the actual capacity of the holding tank of MK II? It is advertised at 18 gallons (see the 2004 manual). I did a test yesterday, and got only 12 gallons (fresh water, nothing else!) into it after pumping it dry. Method: filling a 2 gallon bucket and tipping down the pumpout with aid of a funnel. Overflow as soon as I try to tip bucket number 7 down the pumpout.

Tony

[Ron Hill]

Tony : Not to sure about the MKII, but the MKI has a 27 gal capacity waste tank. 
Guess that newer isn't always better!!

[ssk]

Could it be you were using a Canadian bucket?  ;-)


1 U.S. Gallon = 0.83267 Canadian (Imperial) Gallons
1 Can Gallon = 1.201 U.S. Gallons
1 U.S. Gallon = 3.785 Liters
1 Can Gallon = 4.546 Liters

[tonywright]

Sid, good thought. I will check. That would bring it to 14.4 gallons.

Tony

[John Langford]

I have pondered the possibility of squeezing a larger tank into the space but it doesn't look like it would be worth the effort and cost. Has anyone tried it?

[tonywright]

I have been thinking of different options.

I discovered by looking at some photos that this is a Ronco B212 tank. Definitely 18 gallons. I am thinking that the problem is that I use a pump-out, and not all of the waste/water is being extracted. Ronco suggests that it is necessary to have the pump out plumbing drop below the level of the tank in order to ensure full evacuation of the tank. I think that the plumbing to the macerator would achieve this. So if I take out the macerator, I could maybe figure out a way to loop the plumbing around?

Talking over the problem with a colleague, he suggested adding an extension tank in the second, smaller locker under the port berth, and connected by a large hose at the lowest point of  each. Presumably it could be teed into a common vent.  Could be the easiest way to get extra capacity.

I have added pictures showing the installation of a profile tank monitor. I discovered it is possible to remove the supporting bulkhead to put the foil strips on the tallest straight wall of the tank. A lot easier than putting the foil on the Vee-shaped end.

Tony


Tony

[Craig Illman]

Tony - If you're just sailing in the lake, remove your macerator and fill the space with a B-179 tank like the Mk1's have.

Craig

[Wayne]

My tank has a nice big screw-on cap on top.  I thought mine was 'filling up again' too fast, and suspected that perhaps the pump out wasn't getting to the bottom of things.  Pumped out, opened the cap and checked.  I had only about a cup or two of liquid left in the bottom.  Do you have a way to check that you are really for sure emptying the tank?

[Stu Jackson]

We do not have an inspection port.  The way we check from time to time is to remove the vent line and remove that fitting - same result as Wayne reported.  I note that your vent line, and many others, drops down before it goes up.  Since it's important to keep the vent line clear, I suggest you assure it is free of debris and find a way to support the loop to avoid it filling with refuse and blocking the vent.  Peggie Hall's book about Boat Odors covers heads and holding tanks very well, and is available at www.catalinaowners.com.

The tank WILL fill up rapidly if the shutoff valve to the tank is open when the direct thru hull valve is open at the same time, if your "plumbing" is like that: i.e., head outlet to the overboard discharge thru hull then to a shutoff valve to the tank inlet at the high side of the tank; a separate macerator output hose and valve are always from  the bottom of the tank.

[tonywright]

Stu, it is probably the angle of the camera that makes it look like the vent hose dips. I replaced the standard reinforced PVC with the white "odorless" hose at the same time as installing the tank monitor. It is supported all along the lip of the bunk if you look at picture number 2.

Tony

[Stu Jackson]

Good move, Tony.  Picture 1 had me confused.  This was posted to remind others, too.

[Mike and Joanne Stimmler]

Stu brings up an excellent point with making sure your vent hose is clear. When I was having trouble with my macerator, I found that mine was not clear and it prevented the macerator from working properly.
This was caused by me when I was using a pump out station rather than the macerator, I would flush the tank a few times by filling it until I saw water coming out of the vent pipe. Unknowingly, I was getting some of the crud from the bottom the tank going into the vent tube (mostly toilet paper) and clogging it and a good reason why you should not put toilet paper in your holding tank and also to not completely fill the tank when flushing.

[tonywright]

A math puzzle to stimulate the mind:

I have attached the dimensions of the B212 tank. It is wedge-shaped and tapered to make the exercise fun. I did some calculations of the volume of the tank assuming zero-thickness walls. Then I called Ronco to ask about the typical thickness. Very helpful people there by the way. The usual thickness is at least 1/4 inch, could be more.  So then I subtracted the volume consumed by the walls, and came up with a maximum interior volume of  ... 14.3 US gallons.

Does anyone else come up with a different calculation?

Tony

[Braxton]

I'm not sure if I fully understand your diagram.   What is the wedge shaped section on the bottom right?  Also, what does the line bisecting the lower left diagram represent (the one that shares the 3 1/2 measurement with the bottom right diagram)?

[tonywright]

The diagram is from the Ronco catalog. The top part of the diagram show a plan view (looking down at the top of the tank). The lower left shows a side elevation, and the bottom right attempts to show the end elevation (I think)

Have a look at the photos above it might help. 

The tank is wedge shaped to fit the area along the hull. So looking from the aft end it is 15 inches wide, 11.5 inches tall on the starboard side, and rising to only 3.5 inches on the port side. It tapers from 15 to only 10 inches wide at the front, and the floor rises slightly so that it is only 10.5 inches deep at the front.

Tony