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Author Topic: holding tank redo  (Read 191 times)

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mdidomenico

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holding tank redo
« on: May 06, 2019, 11:35:22 AM »

while i wait for the yard to pull my engine out, i figured i should refocus on the holding tank replumb.

last summer i pulled the tank and all the hoses to the head and macerator.  what a mess.  i flushed the tank out with water and chemicals and left it sitting outside till winter.  i brought it back down to the boat a few weeks ago, with plugs in all the fittings.  sadly, i'm getting a waft of oder from the tank itself, which i'm guessing means the tank itself has permeated and no amount of scrubbing is going to get it clean.

so if i'm looking a new tank, i was wondering if there were any recommendations on a redesign of how all the plumbing and/or tank design should be done.  i see catalinadirect sells the ronco tank which i guess is OEM (seems to look exactly like mine).  before i go ahead and order a new tank, i'm wondering, since i have everything apart if there's a better way to reroute all the piping and whether that would change the design of the tank.

i've already changed out the pumpout fitting, changed out the macerator thru-hull, loped off the vented stanchion, and i'm going to cut a new vent thru-hull soon (haven't figured out exactly where to drill the hole yet though).

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1989 Cat34 #856, original MXP-25(ab?)

KWKloeber

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Re: holding tank redo
« Reply #1 on: May 06, 2019, 11:57:39 AM »

I have NO idea if this is possible on the C34, but on my C30 I added a wet trap on the tank discharge. The purpose is that, once the poo level hits the top of the outlet, a pump out sucks air (literally and figuratively.)
The wet trap letís me completely empty the tank because the vacuum holds until the trap is emptied.   It isnít a huge volume left behind, but every bit helps.  If you use a macerator it makes no difference, so long as it is below the tank outlet.

The tank outlet isnít the lowest point of my hull, so I just ran hard pvc to a point lower than the outlet and made a trap w/ a tee/elbows (w/ a cleanout plug just in case.)   Again, no idea if itís possible in your arrangement but I could post a pic showing it, and knowing that it would be different for you, if itís at all feasible.
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Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
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mdidomenico

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Re: holding tank redo
« Reply #2 on: May 07, 2019, 05:48:49 AM »

if i were to keep the same arrangement in tank dimensions and port locations, i could add a wet trap to the lower outlet and then run it up to the deck.  that's a good idea.

however, my understanding is that newer design tanks have/require a dip tube instead of a straight outlet port.  if i went with a differnet outlet layout with dip tubes, then i'd have to get a tank with less height, which would reduce my holding capacity.  that's not a great option unless i can blow out the divider between the two lockers and make a much longer tank.  but then we're likely talking a custom tank which might be pricey

the original layout of my tank (and likely all other mk1's), is that it has three outlets on the face.  one at the very bottom which was connected to the macerator directly, a second a little higher up that had the pumpout, and third near the top that the toilet connected to.  tank drawing https://www.catalinadirect.com/measurement-drawing-f8016/

my plan was to change things around a little, the lowest hole would be for the pumpout, plumbed with hard pvc until i clear the top of the tank and then hose to the deck fitting.  the second slightly higher hole would connect to the macerator which would be plumbed with pvc & hose and located above the tank in the cubby behind the cushions (high mounting keeps the pump from sitting in the effluent).  and the third hole would remain for the toilet

the reason for the short lengths of hard pvc is to keep effluent out of the hoses and reduce/elimante the risk of permeation.  the only concern i have with this arrangement is whether the macerator will be able to pull the effluent up 12-15" through the pvc, grind it and then discharge (the pump manual says it'll do 4ft dry).  i wont be able to 100% empty the tank with the macerator, but given my sailing area i'm likely to pumpout more often then macerate


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1989 Cat34 #856, original MXP-25(ab?)

kh3412

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Re: holding tank redo
« Reply #3 on: May 07, 2019, 06:10:50 AM »

Did my tank two years ago. Used the original design but removed the  macerator outlet, as on the great lakes. Deal with ronco direct they will remove or add openings were you want. Very good people there.
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