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Old 16-11-2013, 11:46   #16
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I have a valve on the tank
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Old 16-11-2013, 12:17   #17
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I have a valve on the tank
I would lose the tank valve and put in a proper seacock. At least that way you could change the bit of hose that'll be permeated without hauling out.
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Old 16-11-2013, 13:23   #18
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Re: Self Draining Holding Tank or Catch and Release of Blind Mullet?

[QUOTE=Viking Sailor;1329648]A trick I have used to clear waste from the discharge hose is to place a ball valve in the vent hose. With the vent valve closed pumping water into the tank will force out waste stuck in the discharge hose. Also, pumping water into the tank with the tank discharge valve closed and the vent valve open will clear the vent hose.


Great idea ! , I am in the process of a new system and will incorporate this .
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Old 16-11-2013, 14:41   #19
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Re: Self Draining Holding Tank or Catch and Release of Blind Mullet?

G day Raymondr i built my holding tank from ply and epoxy and my idea mirrors yours except that i made my tank with an incline in it ,from memory its about 5 degrees so that all sludge falls towards the outlet,located as close to the bottom and central with the end and my holding tank which btw holds 75 litres and i also fitted a deck pump out pipe because you never know some day you may be up a river system with a ''full load'' so to speak and lastly put a carbon filter on your vent line other wise it will pong .Lastly i tapped into my existing toilet hose when i built my holding tank with a ball valve on the holding tank which led to a ''y'' valve to my existing toilet hose line and it works well for me if i can be of any help just ask cheers Andy
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Old 21-12-2013, 03:58   #20
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Re: Self Draining Holding Tank or Catch and Release of Blind Mullet?

I am fitting out a 46' ketch at the moment and have designed a very similar setup. My primary question: is a vented loop necessary? If the tank is full, the discharge valve must be closed, so no need for the vented loop because there's no connection to sea. If the discharge valve is opened, the holding tank will empty, so a siphon will not commence. Basically, I see the holding tank and its breather valve as a big vented loop.

Two other questions. If the tank fills and head is again flushed, the breather will eventually fill with poo, so what would be the best level indicator or device to warn the tank is nearing capacity? A friend suggested a vacuum style reader similar to that used in washing machines. Most devices I've seen are designed for fuel or other clean fluids, so most likely to gunk up, so a vacuum might be the answer. Or would the head backfill and struggle to flush - to indicating an issue?

Lastly, I was going to place a y-valve on the hose between the tank outlet and the overboard skin fitting. One route would empty overboard, the other would direct to the pumpout. I'd have a separate ball valve on the skin fitting. I could use the pumpout deck fitting to flush pressured water back up the line into the tank to clear blockages.

All good theories, but eager to hear an experienced point of view.

The bottom of the head is regular waterline and one third up the poo tank is the heeled waterline, if that helps paint the picture. I'm using a TMC electric head and have been told it will only pump up 1.5m - when the impeller is new. The top of my tank is currently 1.2 above the base of the head, so I'm trying to steal back every centimetre I can. A vented loop will cost me 15cm. If it's not needed, I could possibly plumb into the side of the tank at the top, rather than looping over and that will save me even more precious cms.
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Old 21-12-2013, 05:18   #21
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Re: Self Draining Holding Tank or Catch and Release of Blind Mullet?

It's not needed. You are right.

We have the same set up but the pump out goes into the top of the tank and the bottom of the tank is 50 cm above the waterline and self drains to the ocean.

The only vented loop is the water intake.
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Old 21-12-2013, 05:18   #22
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Re: Self Draining Holding Tank or Catch and Release of Blind Mullet?

No Y valve.
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Old 21-12-2013, 09:02   #23
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Re: Self Draining Holding Tank or Catch and Release of Blind Mullet?

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Hi There,

I'm thinking of making a self draining holding tank (only about 20 liters or so), and was wondering if anyone else has done this and what issues you may have had.

As good as it sounds there will be problems.
I had the same idea and system but I ended up ripping it out 6 months into our cruise after I think Clog No 7 or was it 8.

The problem is that in a real life full time live aboard situation with crew aboard the waste has no real time to break down into enough of a slurry so that it will flow out the bottom. Sure you can add holding tank addatives but how much of that are you going to carry South with you because you won't find that on a shelf in Mexico!

The waste needs time to break down....if you don't give it that time....you will be unclogging it all the time and ripping it out.
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Old 21-12-2013, 09:52   #24
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Re: Self Draining Holding Tank or Catch and Release of Blind Mullet?

> the waste has no real time to break down into enough of a slurry so that it will flow out the bottom

The OP said he currently has a macerator.
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Old 21-12-2013, 09:57   #25
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Re: Self Draining Holding Tank or Catch and Release of Blind Mullet?

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> the waste has no real time to break down into enough of a slurry so that it will flow out the bottom

The OP said he currently has a macerator.
Yes, but if the macerator is installed on the exit of the tank, you will still have the same problem. The poor blender needs to be installed betwen the head and the tank. I've played that game and lost.
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Old 21-12-2013, 10:14   #26
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Re: Self Draining Holding Tank or Catch and Release of Blind Mullet?

I think StuM's point is that the OP has a macerating toilet.
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Old 22-12-2013, 09:15   #27
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Yes, but if the macerator is installed on the exit of the tank, you will still have the same problem. The poor blender needs to be installed betwen the head and the tank. I've played that game and lost.
Funny, we've never had a clog in ours, and don't have a maceratator on the boat. 15 gallons of poo, water, and tp. But I did put a valve immediately on the tank exit to prevent everything from settling out in a section of hose before the seacock.
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Old 22-12-2013, 09:37   #28
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Re: Self Draining Holding Tank or Catch and Release of Blind Mullet?

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Funny, we've never had a clog in ours, and don't have a maceratator on the boat. 15 gallons of poo, water, and tp. But I did put a valve immediately on the tank exit to prevent everything from settling out in a section of hose before the seacock.
Well I always said my crew was full of S$#!.
I think it was due to the head use volume in my case. With a few of 4 and two teenagers, well that is a lot of material in a short amount of time going into the system.
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