Holding tank waste back flow. Why?

[cmedsailor]

The holding tank in my boat is installed above the toilet. After where the discharge pipe exits the toilet there’s a V valve where you can direct the waste to the top of the holding tank or to the outlet seacock. To use the holding tank obviously you need to close the outlet seacock (there's only one). I can use gravity to empty it when opening the seacock.
Sometimes (not always; and this makes it even more strange) when I discharge into the holding tank I have backflow from the holding tank to the toilet. Why this happens? Jabsco instructions say that I need to install a vented loop on the discharge pipe above the holding tank. But is this necessary? Could this be the reason? The vented loop is needed to allow air in the system so the flow stops. But I believe the vent pipe of the holding tank can do this. It’s on the top of the tank and there’s always air there. Or could it be a problem with the valve gasket and joker valve? I have replaced the whole pump (twist n’ lock) about a year ago but I think their parts, especially under the hot sun of the Med, don’t last very long.
Any suggestions?
And a further question: Since there's only one outlet seacock when there's no need to use the holding tank and can discharge directly to the sea I have the option to keep the V valve at any position (ie discharge in the sea directly or through the holding tank). However I almost always leave it directly to the sea. Is there any reason to discharge through the holding tank? Is there any possibility to have back flow of sea water so leaving it via the holding tank will minimise this risk?

 

[Talulah]

I don't see any point in your first 'V'.
Have all the contents go through the holding tank and have the holding tank sea cock open/closed as you wish. You will then have no need for the anti-syphon loop.
The only issue I can see is if the top of the holding tank isn't high enough when heeled.
You could get water pushed up into the Holding Tank back filling it that way.

 

[nigelmercier]

To use the holding tank obviously you need to close the outlet seacock (there's only one)...

I don't follow this: only one outlet seacock, for the tank and direct? How would that work?

 

[prv]

Is the backflow just what's in the pipe falling back down through a worn joker valve, or does it keep coming out of the tank? If the latter, I guess the pipe goes into the top of the tank but has a dip tube down to the bottom and so is able to set up a siphon since the tank is above the toilet. A siphon break ought to help with that.

I don't think you need a siphon break to stop the sea flowing in through an above-waterline tank - the tank and its breather will act as a giant siphon break.

If in your direct-overboard configuration you have a pipe from toilet to sea with no siphon break in it, then you do have a risk of the sea coming in. How likely will depend on the height of any loop, but it will always be possible.

Pete

 

[cmedsailor]

I hope the attached will help.
I don't think that the backflow is just what's in the pipe. It can fill the bowl. On the other hand when I use the holding tank I can actually hear to the waste dropping (during pumping) into the tank. So it doesn't sound like the pipe has a dip tube.

Pete, from your last sentence "If in your direct-overboard configuration you have a pipe from toilet to sea with no siphon break in it, then you do have a risk of the sea coming in. How likely will depend on the height of any loop, but it will always be possible" I guess it will be safer to direct the waste ALWAYS through the holding tank then.

 

[vyv_cox]

If sewage is running back into the toilet it has to be the joker valve at fault. Calcification of the valve is common on live aboard boats. Hydrochloric acid is cheap and widely available in the Med. dose your toilet every couple of weeks and the problem will be solved.

 

[vyv_cox]

I don't follow this: only one outlet seacock, for the tank and direct? How would that work?

Diverter valve? the RM69 wrap around tank includes this, discharge through one seacock. Toilet can discharge overboard or to the tank.

 

[VicS]

I hope the attached will help.

not until I realised it was upside down

Vyv is right in that the joker valve must be allowing effluent back in to the bowl. Cleaning that will hopefully solve the problem.

Fitting one of the "Twist and lock" pumps should eliminate the problem regardless of any slight back flow through the joker valve.

Since you feel that the back flow is more that what is in the pipe I'd deduce that what you call the "V valve" is not 100% effectively closing off the branch to the sea-cock. It is allowing effluent to flow from the tank via the Y fitting and the joker valve back into the bowl.

 

[cmedsailor]

Fitting one of the "Twist and lock" pumps should eliminate the problem regardless of any slight back flow through the joker valve.
.

But I do have a twist and lock pump.

 

[MoodySabre]

I have only one discharge seacock too and a diverter as the OP describes. The top of the tank is higher than the loo so sometimes some tainted water has filled up the bowl when someone has forgotten to twist & lock. Generally not a problem and only so when the tank is nearly full.

 

[VicS]

But I do have a twist and lock pump.

Sorry I missed that. That's not working properly then

 

[Stu Jackson]

Heads pumps can usually move the contents about 6 feet. I agree the joker valve is suspect. When was the last time you serviced the heads pump assembly? Completely?

 

[Stork_III]

Heads pumps can usually move the contents about 6 feet. I agree the joker valve is suspect. When was the last time you serviced the heads pump assembly? Completely?

The tank breather could be blocked allowing back pressure to force passed the Joker valve.

 

[RupertW]

Heads pumps can usually move the contents about 6 feet. I agree the joker valve is suspect. When was the last time you serviced the heads pump assembly? Completely?

We have a similar setup but without any direct access. I think it's the water/wastein the outlet pipe leading up to the top of the tank, and that is a considerable amount compared to the bowl capacity. We have twist and lock but it is clearly not working completely. Have done a basic decalcification of the visible bits of the pump which helped a little.

Our main issue is that if you pump lots of water through to ensure that any flowback is clean while the outlet seacock is shut then the holding tank doesn't allow for much more than 36 hours of use before filling up. Fine mostly but does limit the amount of time you can spend in that prime spot in a nice anchorage.

I'll try the hydrochloric acid tip if I can work out the Croatian for it.

 

[cmedsailor]

Heads pumps can usually move the contents about 6 feet. I agree the joker valve is suspect. When was the last time you serviced the heads pump assembly? Completely?

How do you service the pump? Besides flashing fresh water, some olive oil left from the salad (not often) I don't do anything else.

 

[vyv_cox]

The tank breather could be blocked allowing back pressure to force passed the Joker valve.

I would have thought that back pressure would improve the effectiveness of a joker valve, in that it would force the lips closed. When they are old the lips tend to remain open as the rubber deteriorates.

 

[Dockhead]

IMHO you are asking too much of your joker valve to keep the whole contents of your holding tank out of your toilet. In my experience they never keep a perfect seal for long, no matter how calc-free you keep them. And the twist-n-lock jobbie doesn't really lock, in my experience.

Your analysis of the vented loop situation is correct, in my opinion- a vented holding tank should prevent syphoning. But if I were you, I would consider a vented loop for a different reason - to keep your holding tank contents from pressing against your joker valve. That way the only liquid which will seep past your sooner or later seepy joker valve will be the last, clean, flush water, so no harm done.

"Joker valve" - aptly named, as far as I'm concerned.

P.S. If your diverter valve bypasses the holding tank, and there is no vented loop between it and your toilet, that is dangerous. Another reason to put in a vented loop. Put it in ahead of the diverter valve and you will kill two turds, err, two BIRDS, with one stone.

 

[cmedsailor]

Put it in ahead of the diverter valve and you will kill two turds, err, two BIRDS, with one stone.

That sounds interesting but I could never place it above the holding tank. And anywhere below will, I guess, will not work.

 

[johnphilip]

Correct installation?

HaveI misread the posts or is the diverter valve below the tank? if so an arrangement such as picture 2 on the attached TEK TANKS page works fine for me and may be better. When imstalling the tank last year I did take the opportunity to fit a service kit, including the joker valve at the same time.
http://www.tek-tanks.com/boats/sanitation-systems/holding-tank-plumbing-and-layouts/

 

[vyv_cox]

IMHO you are asking too much of your joker valve to keep the whole contents of your holding tank out of your toilet. In my experience they never keep a perfect seal for long, no matter how calc-free you keep them.

OP says the hose from the toilet goes to the top of the tank. The joker valve only supports the weight of liquid in the upwards leg of the loop, same as any other installation.