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Old 09-08-2007, 08:38   #1
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Holding Tank Pumpout

I've been having trouble with pumping out the holding tank for 10 years. I've replaced impellers, macerator pumps, hoses, Y-valve, etc. Would work for 1-2 pumpouts, then stop. After all this time, I just realized that the system does not have a vented loop. Since I pump out thru a seacock, is it possible for this to hamper the pumps operation, because of the siphoning effect. Also, when I thought the pump was not working, maybe it was siphoning seawater back into the tank. What do you think? Will a vented loop solve this problem?
Marc
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Old 09-08-2007, 09:04   #2
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I'm visualizing your system as the following: toilet pumps its load to a Y-valve. One direction is directly over the side via an underwater thruhull, the other direction is into a holding tank. That's assumption one.

Assumption two is that the tank is vented to the atmosphere with, at least, a 1/2" hose. Assumption three is that the discharge end of the holding tank is at the bottom of the tank. Assumption four is that you have a macerator pump in the discharge hose prior to the seacock and underwater discharge? Assumption five is that you have no deck discharge fitting.

Are these assumptions correct, before I shoot my mouth off?
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Old 09-08-2007, 09:15   #3
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Toilet pumps to holding tank. Holding tank discharges to Y-valve which directs flow to either deck fitting, or to macerator pump then out thru seacock. I think that between the macerator & seacock there should be a vented loop. Is that right?
Marc
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Old 09-08-2007, 10:27   #4
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If the holding tank is below sea level, yes, there must be a way to break the siphon should the macerator allow water to flow back into the holding tank after pumping. Personally, I hate macerator pumps. When they leak, saltwater gets into the motor and destroys it. And worse stuff then leaks all over the bilge. Yuck! My system uses a holding tank ABOVE the water line so that gravity takes care of the transfer, not mechanical systems.

So, to answer your question, yes, you will need a loop above sealevel AND a siphon break between the macerator and the seacock. If the siphon break vent is inside the boat, it will spray a small enough amount of air and yuck to make your boat smell like an outdoor toilet. Get a hose barb fitting installed on the siphon break (plastic is just fine), and put a vent to the outside as high above the deck level as is convenient. Don't route it overboard below the deck level or it could fill when you are heeled.

Again, if there is anyway to relocate your holding tank (including rebuilding it into a custom and little used space) ABOVE the waterline, that will help. If you go completely nuts, you could eliminate the macerator pump (source of much economic gain by folks such as me and the engineers who designed it in the first place) by installing a LAVAC toilet. It uses a simple hand bilge pump (they supply a Henderson, I use a Whale 10) to empty the bowl, macerating the toilet paper and "product" before they enter the holding tank. Then, forget about the Y-valve as well, simply place a tee-fitting into the discharge hose prior to the seacock, route the hose to the deck fitting, and voila! You will have eliminated the need for macerator pump, Y-valve, siphon break, siphon vent line, and all of the problems associated with all of the above.

Sorry to sound like a proselytizer for LAVAC, but everyone I know who has made the switch begins to get a bit goofy about them. You would still need a siphon break for the seawater INTAKE if the toilet bowl is below water (especially when heeled). Mine is above water all the time, so it's not an issue.
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Old 09-08-2007, 11:54   #5
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A siphon-break (vented loop) is installed in the (below waterline) overboard discharge.
Info:
http://www.tc.gc.ca/MarineSafety/tp/...-Appendix3.pdf
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Old 09-08-2007, 12:10   #6
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Go for an airhead.
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Old 09-08-2007, 13:39   #7
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Quote:
Originally Posted by Louis Riel
Go for an airhead.
Brent
These things look great on paper but... it sure looks like a large step up to the pot for my wife and kids. I've never seen one in person but they do look very tall...
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Old 09-08-2007, 16:49   #8
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Quote:
Originally Posted by marc
I've been having trouble with pumping out the holding tank for 10 years. I've replaced impellers, macerator pumps, hoses, Y-valve, etc. Would work for 1-2 pumpouts, then stop. After all this time, I just realized that the system does not have a vented loop. Since I pump out thru a seacock, is it possible for this to hamper the pumps operation, because of the siphoning effect. Also, when I thought the pump was not working, maybe it was siphoning seawater back into the tank. What do you think? Will a vented loop solve this problem?
Marc
Although a vented loop is the proper installation, unless your description of the problem off, I don't think a vented loop will solve your problem. The pump should be able to pump fluids without a siphon break. A siphon break keeps fluids from coming back in. Is the problem intermittant, or does it really only work for a couple of pumpouts after replacing parts and then fails? What exactly do you mean by fails? Do you have some means to see if the tank is empty? Is the tank emptying, then refilling later? Do you see air bubbles in the water near the through hull when the tank is empty? Do you close the seacock after you have pumped out?

If it really only works a couple of times, and then does not pump, are you burning out impellors from too much lift or running dry too long?

To be a siphon problem the tank will be empty right after you pump and there are multiple failures happening to cause the tank to refill.

1. If the hose from the holding tank to the seacock is always under the waterline (worst case and not even really a siphon), then the water has to leak back into the holding tank through the sea cock, pump, and Y valve. How do you set your valves when you are done pumping?

2. If the hose goes above the waterline at some point and you pump out until there is air in the lines, then you don't have a siphon until it fills with water by heeling, pounding or whatever mechanism. Then see 1. above.

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Old 09-08-2007, 21:39   #9
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Vertical distance...

What would the maximum vertical distance that the pump has to lift the sewerage?

Is it possible that there are air leaks in the piping?
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Old 09-08-2007, 21:48   #10
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Just chiming in that I love my Lavac :-)

Rebel Heart - The boat and her crew - Eric's Blog - - Head install weekend is over, successfully.
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Old 09-08-2007, 23:05   #11
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The tank is mostly below the waterline. The ditance from the bottom of the tank to the pump is about 3.5'-4' .When trying to isolate the problem, I disconnected the outlet hose from the pump, and the pump worked OK, so I thought the hose might be clogged or kinked, so I changed it. It worked at first, but when the fluid level in the tank went down about 5"-6", it stopped. I couldn't figure out why. Quite a while later I realized that was the waterline level. After looking at some installation diagrams online, I saw that the only thing different about my hookup is that I don't have a vented loop. Could this be the problem? I think I have to try one to find out for sure, or am I wasting my time?
Marc
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Old 09-08-2007, 23:08   #12
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By the way, I do have a Lavac head with an elec. flush. Works great.
Marc
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Old 10-08-2007, 00:35   #13
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Check your pump specifications...

I suggest checking your pump specifications.

4' - 5' is quite a long way for a pump not designed for lifting.

Have you considered a diaphragm pump?
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Old 10-08-2007, 01:23   #14
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Quote:
Originally Posted by marc
The tank is mostly below the waterline. The ditance from the bottom of the tank to the pump is about 3.5'-4' .When trying to isolate the problem, I disconnected the outlet hose from the pump, and the pump worked OK, so I thought the hose might be clogged or kinked, so I changed it. It worked at first, but when the fluid level in the tank went down about 5"-6", it stopped. I couldn't figure out why. Quite a while later I realized that was the waterline level. After looking at some installation diagrams online, I saw that the only thing different about my hookup is that I don't have a vented loop. Could this be the problem? I think I have to try one to find out for sure, or am I wasting my time?
Marc
Anything is possible, I've been amazed at some of the fixes that make no sense to me. Try breaking it down to a simple problem. If you have the typical macerator pump, it is a rubber impeller pump with knives in front. Ignore the knives for now. Go buy a Jabsco drill motor impeller pump, stick the intake in a bucket of water and start the pump. Try different positions for the outlet. Does there need to be a vented loop on the output for the pump to work in any of the positions? What will keep the pump from working? Try lifting the pump high above the bucket and start it with air in the intake hose. Try poking some holes in the intake hose above the water. Try running the pump dry for several minutes, then see how well it pumps.

The distance of 4', is that total length of hose, or vertical distance? The Jabsco pump claims self priming to 4' vertical when dry.
http://www.jabsco.com/files/18590_se..._macerator.pdf

The tank emptying to waterline level will happen with no help at all as long as the valves are open and all the hose is below water level, and if the hose does go above water level someplace, once you filled the hose with liquid, the holding tank would empty out down to waterline level without the pump, as that is a siphon. A siphon break will stop that from happening. Actually if the pump is in good shape, very little if any water should be getting by it in either direction while it is not running. If the pump is running but won't pump the tank below waterline level it is basically just getting the vanes out of the way of the siphoning action and producing no effective pumping.

When you said the pump was working, did it pump the number of gallons per minute speced into a bucket? Were there lots of air bubbles?
I first thought that Boracay's idea of an airleak on the suction side wouldn't pan out because there would be sewage in the boat, but if the leak is in a place above where liquid would pool, then you wouldn't have the sewage problem. And Y valves can leak which could also introduce air from unexpected directions.



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Old 13-08-2007, 16:02   #15
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Well, evryone that said that the addition of a vented loop in the system would not help,WAS RIGHT. So it was back to the drawing board for me. I finally hooked up a temporary disharge hose from the pump,up and over the side. It worked. Filled the tank 3 times (with water), and at worked every time. So I re-routed the discharge hose to exit about 16" above the waterline & under the bridgedeck (forgot to mention it's a catamaran). I guess the system wasn't designed to pump out below the waterline. I hope this "fix" will solve my 10 year problem.
Thanks for all the helpful advice,
Marc
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