Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 11-01-2012, 12:29   #16
Registered User

Join Date: Dec 2011
Posts: 6
Re: Gravity holding tank won't drain

Quote:
Originally Posted by Ben 331 View Post
I'm looking at revising my head/holding tank arrangement, and would appreciate any/all advice. Please note that I live in Canada where pumping overboard is allowed in open water.

The Jabsco manual head on my sailboat pumps into the top of a holding tank; the holding tank drain goes to a 'Y' valve, which directs it to either a deck pump-out, or out of the boat via the through-hull. The tank is well above the water line, so when I replaced the hoses etc. I confirmed it could drain well by simply having the Y-valve in the right position and opening the through-hull. However, in practical use - as in our recent summer vacation - it would not drain, but became plugged as the solids in the tank had collected on the bottom, at least partially blocking the drain. All waste hoses are standard 1.5" and new. I was able to do the unclogging but will not dwell on the details here - just let it be said that I am keen on avoiding this scenario again.

I'm considering one of the following options:

1) Installing an macerating head - if the waste was macerated before it got into the tank there should be much less chance of blockage; the downside is I'll have to wire in a circuit for it and have more things to drain my batteries and possibly breakdown. Space is also an issue, as most of the electric heads I've seen are larger than my current Jabsco Twist-Lock, and I'm not sure that they'd fit.

2) Installing a manual or electric pump to drain the tank - pulling the waste out, instead of just relying on gravity, would hopefully allow the tank to be emptied reliably. Downside here is that the pump would have to be at least 2-3 feet downstream of the tank, and I'm not sure if additional suction would empty the tank, or just make the clog worse by pulling more stuff into the hose. Space is an issue here too, since the only place to mount the pump would be under the sink and that space is already full of plumbing.

Any advice on which of the options would be a better choice? Are there any other alternatives I should be considering? Thanks!
Hi Ben,
first keep the instalation as simple as possible try not to have hard bends anywere in the system,a tank with an inspection hatch is a must sooner or later you will need to get in there.Also the deck out if possible vertical above the tank.
what enters the tank enters as sludge the problem starts when you leave it, the liquid seperates up and in the bottom it sets solid,in use three plans of attack first bio chemicals for the caravan do break things up it takes a few days, i have also fixed up a length of rigid tube to a hose connector it works well prodding things free,and finally the only good pump that works is a diaphram pump you need suction and lots of it.your only comfort is to know that all of us have had or will have the same problem.
good luck
__________________

__________________
scoch is offline   Reply With Quote
Old 11-01-2012, 12:40   #17
Registered User

Join Date: Jan 2008
Posts: 165
Re: Gravity holding tank won't drain

you can also buy a product used for septic tanks and leech lines that contains a bacterial culture that eats up the sludge and scale that builds up in holding tanks. We have used it very successfully in the past. It can be instilled either via the toilet or the inspection plate of the tank.
__________________

__________________
S/V Katabatik
Leopard 46
San Francisco, CA
stacy is offline   Reply With Quote
Old 11-01-2012, 12:46   #18
Senior Cruiser

Cruisers Forum Supporter

Join Date: Mar 2007
Location: Santa Cruz
Boat: Boatless Again
Posts: 4,321
Re: Gravity holding tank won't drain

Make sure that you flush the tank with at least 25-30 toilet pumps of seawater every time you empty it. The flushing tends to prevent buildup of solids at the bottom of the tank.

If you have a clog, the vacuum on a pumpout station may pull it through. Otherwise you can use a water hose sealed with a rag to inject water back into the outlet of the tank to loosen things up, but watch out you don't overfill the tank...
__________________
donradcliffe is offline   Reply With Quote
Old 11-01-2012, 18:10   #19
Registered User
 
Ben 331's Avatar

Join Date: Jan 2012
Location: Vancouver, BC Canada
Boat: Beneteau 331
Posts: 6
Re: Gravity holding tank won't drain

Thanks for all the responses ! I'll attempt to answer the questions that were raised in the discussion:

Rebel Heart:
Actually the contents of the tank had only been in there for a day or two - the tank fills while we stay in an anchorage... when it's full we leave and empty it out in open water. The tank capacity is about 30 gallons.

Jack Dale:
There's no scale build-up in the tank (I had it all out of the boat at the start of the season), and the hoses are new so don't believe that build-up is my problem.

Cheechako:
I don't think we use a lot of paper - I've instructed the family to
flush often and pump lots of water through. (I'm also afraid that if I
deliver any more lectures on paper use my next trip will be solo.)

PegHall:
The holding tank discharge line is in the bottom of the tank - from there it turns 90 degrees to go horizontally forward a couple of feet and then meets the Y-valve, and from there to the thru-hull. The sharpest bend in the line is - unfortunately - right where it exits the tank to go forward - probably a 4" radius.... there are other bends but they're smoother. The tank was getting flushed regularly (and rinsed out after emptying); from your explanation the plumbing layout seems to be the root cause.
Unfortunately, the layout would be difficult to change - the holding tank is directly behind the head, while the thru-hull is under the vanity, which I believe is a fairly common configuration on sailboats of this size. Questions - if I was able to find space for a pump, what type would you recommend ? I saw from one of your previous posts that you suggested an electric diaphragm pump - instead of a macerator - since they don't burn out as easily if they're run dry, and tend to be more reliable. I believe the ideal location of the pump would be as close as possible to the holding tank - but in my case it would have to be mounted about 3 feet downstream - after the Y-valve and before the thru-hull. Would a pump in that configuration still be able to empty the tank OK ? Or could it just create worse clogs in the hose?Many thanks !
__________________
Ben 331 is offline   Reply With Quote
Old 11-01-2012, 19:13   #20
Registered User

Join Date: Aug 2011
Location: Melbourne Australia
Boat: Paper Tiger 14 foot, Gemini 105MC 34 foot Catamaran Hull no 825
Posts: 1,616
Re: Gravity holding tank won't drain

I dont know how legal it is,
But the previous owner didnt use the holding tank and neither did I, No smells,

I have a macerator and discharge straight out through the below waterline thru hull.
It comes out as a brown stain in the water, with no solids, Couple of minutes and it is totally gone,
I also have a salt water flush, So I can pump as much seawater through it as needed,

If you have a freshwater flush, You run out of water very quickly,
__________________
Mr B is offline   Reply With Quote
Old 11-01-2012, 19:22   #21
Senior Cruiser

Cruisers Forum Supporter

Join Date: Mar 2006
Location: Nevada City. CA
Boat: Sceptre 41
Posts: 3,745
Images: 9
Re: Gravity holding tank won't drain

I would suggest that you change the 90^ bend to 2-45^ bends if you can. This is what we do in plumbing and it makes the flow work better. For a pump I would use one of the hand pumps. My system is not gravity but the pump does a good job of pulling all of the waste out of the holding tank. If someone doesn't post it here I'll look at the boat this weekend and give you the name. We have a rule on our boat that takes some getting used to. Nothing goes in the toilet unless it goes through your body first. To this end we have a zip loc bag that we keep in a container next to the toilet and we put the toilet paper in there.
__________________
Fair Winds,

Charlie

Between us there was, as I have already said somewhere, the bond of the sea. Besides holding our hearts together through long periods of separation, it had the effect of making us tolerant of each other's yarns -- and even convictions. Heart of Darkness
Joseph Conrad
Charlie is offline   Reply With Quote
Old 11-01-2012, 19:53   #22
Marine Service Provider
 
peghall's Avatar

Community Sponsor
Cruisers Forum Supporter

Join Date: Feb 2011
Posts: 1,533
Re: Gravity holding tank won't drain

The holding tank discharge line is in the bottom of the tank - from there it turns 90 degrees to go horizontally forward a couple of feet and then meets the Y-valve...from your explanation the plumbing layout seems to be the root cause.

Yup...That is what's causing your problem. Ya GOTTA have a vertical drop to the thru-hull for gravity discharge to work...and you have a horizontal run. Without any help from gravity or a pump to push sludge through the line, it's just gonna sit there and build up. So if you can't replumb to create a straight drop, you'll need a pump. I'd go with either manual or electric diaphragm...the SeaLand T-Series pump.

When it comes to installing any pump, if I were you I'd treat the whole installation as if the idea of gravity discharge never entered your mind. Put the y-valve as close to the tank as possible and still be readily accessible. Then the pump, which I'd put fairly high...any pump--macerator, diaphragm, manual or electric should be able to handle at least 4' of head...you won't need to put it THAT high. Then the pump will get an assist from gravity to empty the tank.

You'll still need to put lots of water through the system to keep it rinsed out...maybe not EVERY time you pump out or dump, but at least every other time.
__________________
2017 Peggie Hall
Specializing in marine sanitation since 1987
Author "The NEW Get Rid of Boat Odors"
https://www.amazon.com/New-Get-Rid-B...dp/1892399784/
peghall is offline   Reply With Quote
Old 11-01-2012, 20:19   #23
Registered User
 
muskoka's Avatar

Join Date: Jun 2006
Location: Sai Kung, Hong Kong
Boat: FP Lavezzi 40 / Hatteras 48
Posts: 775
Re: Gravity holding tank won't drain

We have a gravity discharge which works fine. There are a few things which I think help:

1. Our discharge pipe is 65mm.
2. The discharge pipe is about 800mm long, straight out the bottom of the tank then does a 45 degree curve to the outlet. Radius of the elbow is 300mm.
3. We only empty when the tank is at least 2/3 full. I think there needs to be a certain amount of pressure to get the correct flushing action. If necessary, take a couple of buckets of seawater and pour them down the deck pump out.

We lived on our boat for 1 1/2 years without any problem. And we've weekend sailed her for 2 1/2 years, likewise without problem.
__________________
muskoka is offline   Reply With Quote
Old 16-01-2012, 00:04   #24
Registered User
 
Ben 331's Avatar

Join Date: Jan 2012
Location: Vancouver, BC Canada
Boat: Beneteau 331
Posts: 6
Re: Gravity Holding Tank Won't Drain

Thanks for the additional info. I'm now convinced I need to change the plumbing on the holding tank. If I plug the drain in the bottom of the tank, and install a fitting and pump-out that reaches down to the bottom of the tank from the top, I'll be able to route the hose more smoothly, and should also have enough room to add a waste pump and stop relying on gravity. I'm thinking of attaching a 'Y' fitting at the top of the pump-out, so that both the deck pump out and waste pump are connected to it. The benefit in this would be that any potential blockage in the pipe going into the tank could be cleared via the deck pump out fitting. My only concern is if the suction from a deck pump-out could potentially damage the waste pump, since the suction would be applied to all components connected to the tank, including the pump. Any thoughts or recommendations appreciated!
__________________
Ben 331 is offline   Reply With Quote
Old 16-01-2012, 10:33   #25
Senior Cruiser
 
rebel heart's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Posts: 6,190
Images: 3
Re: Gravity Holding Tank Won't Drain

Quote:
Originally Posted by Ben 331 View Post
Thanks for the additional info. I'm now convinced I need to change the plumbing on the holding tank. If I plug the drain in the bottom of the tank, and install a fitting and pump-out that reaches down to the bottom of the tank from the top, I'll be able to route the hose more smoothly, and should also have enough room to add a waste pump and stop relying on gravity. I'm thinking of attaching a 'Y' fitting at the top of the pump-out, so that both the deck pump out and waste pump are connected to it. The benefit in this would be that any potential blockage in the pipe going into the tank could be cleared via the deck pump out fitting. My only concern is if the suction from a deck pump-out could potentially damage the waste pump, since the suction would be applied to all components connected to the tank, including the pump. Any thoughts or recommendations appreciated!
If you have a properly sized holding tank vent (read: bigger than the tiny little line you're supposed to use) it will do a lot to mitigate that problem. A 1/2" or better (some folks are running 1" - 2"), depending on the bends and twists of the line, should be able to alleviate much of the negative pressure inside the holding tank.
__________________
rebel heart is offline   Reply With Quote
Old 16-01-2012, 12:33   #26
Registered User

Join Date: Nov 2011
Location: Marco Island, Florida
Boat: Passport 40
Posts: 81
Re: Gravity Holding Tank Won't Drain

I had the same problem with my Passport 40 and solved it with a rather simple change. I have not had a problem in 25+ years. The change is as follows:

- remove the inlet hose from the top of the tank and plug the tank inlet.
- take the inlet hose and tee it into the hose outlet hose which leads from the outlet of the tank to the thru hull.
- install a valve in the hose which is the arm of the tee which leads into the inlet of the tank.

The idea is to fill the tank from the bottom and drain from the bottom and use the hand pump on the head to free any blockages. To use the holding tank close the thru hull and open the aforementioned valve. This will allow you to pump the waste into the tank. To empty the holding tank, open the thru hull and let it drain out the bottom of the tank. If a clog occurs close the thru hull and pump water with the head pump to clear the clog. Open the thru hull and let it continue to drain. If the clog is at the thru hull close the aforementioned valve and use the hand pump to clear the blockage.
I mention this in my web site Passport 40 S/V Grendel | Passport 40 Sailing Vessel Grendel
__________________
hgd137 is offline   Reply With Quote
Old 28-10-2012, 00:06   #27
Registered User
 
Ben 331's Avatar

Join Date: Jan 2012
Location: Vancouver, BC Canada
Boat: Beneteau 331
Posts: 6
Re: Gravity Holding Tank Won't Drain

This story has a happy ending... Based on the advice above I installed a Jabsco diaphragm pump on the discharge line right below the tank outlet. I also added a pump-out port at the top of the tank (with a tube extending to the bottom), as this allowed me to remove the Y valve altogether, simplifying the discharge plumbing. Since these changes were carried out I've never had a problem emptying the tank - just open the thru-hull and turn on the pump. Excellent!
__________________
Ben 331 is offline   Reply With Quote
Old 28-10-2012, 09:31   #28
Registered User
 
stillbuilding's Avatar

Join Date: Jan 2008
Location: Hong Kong
Boat: Custom Freya 20m
Posts: 961
Re: Gravity Holding Tank Won't Drain

Well I hope this is still a happy ending for you. The design advice given above sounds good.

With the aim of extra insurance to prevent this happening in my own vessel can I get some feedback on this idea as a way of minimizing the solidification in holding tanks.

Would in be useful to have a separate circuit with a high pressure pump circulating the contents of the holding tank? Could be switched on automatically for a few minutes whenever a toilet is flushed or manually whenever I was passing by a switch. Simple enough to incorporate and could be a macerating pump.

I know some smaller sewage processing units have a circulating pump. Useful in a holding tank or not?
__________________
stillbuilding is offline   Reply With Quote
Old 29-10-2012, 12:36   #29
Registered User
 
Ben 331's Avatar

Join Date: Jan 2012
Location: Vancouver, BC Canada
Boat: Beneteau 331
Posts: 6
Re: Gravity Holding Tank Won't Drain

Hi Stillbuilding - as long as the holding tank is emptied or pumped out after each use I don't believe a recirculating pump is necessary. When the boat is in use, normal movement keeps everything sloshing around and in suspension, so as long as its emptied - and not left to settle - everything will be fine. If it's not emptied, there will be other problems besides potential clogging, like the smell permeating the hoses, growth of bacteria and associated odours, etc.
__________________
Ben 331 is offline   Reply With Quote
Old 07-01-2016, 18:58   #30
Registered User

Join Date: Jul 2011
Location: South San Francisco
Boat: Atkins Thistle 32 ft
Posts: 54
Re: Gravity Holding Tank Won't Drain

A regular shot of vinegar&oil in the head will help keep things flowing freely. When I first started doing this, I got an unbelievable amount of salt?/calcium? deposits out of the tank and hoses.
Plug the vent and flush the head till the tank is pressurized (watch it - not too much!) and things may flow.
If your deck pumpout tees into the tank to seacock drain line, alternating between the garden hose and the suction hose at the pumpout may loosen things up.
__________________

__________________
IolantheSF is offline   Reply With Quote
Reply

Tags
gravity-out, holding tank

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Is Gravity Discharge Possible from a Blackwater Holding Tank ? Unicorn Plumbing Systems and Fixtures 27 02-09-2014 07:08
Holding Tank Odor . . . Help ! Phogan Plumbing Systems and Fixtures 40 16-05-2014 14:38
Gravity Holding Tank Installation Questions RHoodJr Plumbing Systems and Fixtures 30 11-01-2012 19:38
Converting a Water Tank to a Holding Tank royelshort Powered Boats 0 16-11-2011 17:06
Head Odors Sailagain Plumbing Systems and Fixtures 19 15-07-2011 11:06



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 00:17.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.