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Old 10-21-2018, 08:05 PM   #1
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Holding Tank Not Fully Emptying

I have a 1990 Grand Banks 32. 25-gallon heavy duty plastic tank. When using the dock pumpout it only empties to about the 50% level. My level indicator (external) works so I know that when the dock pump stops pulling anything else out, I can put about 10 gallons of water back in before the tank is full again. Do I really have 15 gallons of semi-sludge in there? Hard to believe. A bad pickup tube inside the tank? Plastic doesn't corrode but who knows...
All thoughts and suggestions gratefully accepted.
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Oldersalt
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Old 10-21-2018, 08:23 PM   #2
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Are you sure that the tube inside is plastic? If the tube went all of the way to the bottom and was encased in sludge you wouldn’t get anything out of it I wouldn’t think? I thought the original tubes in the GB’s were metal and corroded causing the problem that you seem to be having.
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Old 10-21-2018, 08:33 PM   #3
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Where does the pump out hose come off the tank? If it is on the top of the tank, it very well could be a correded pickup tube inside the tank.
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Old 10-21-2018, 08:42 PM   #4
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I agree with the above folks. You should pull the dip tube and take a look. If metal, replace it with pvc and a uniseal (search Peggy Hall’s responses to older threads). Also, when you have the dip tube pulled you can “stick” the tank to determine if it’s solid or liquid. Probably the later.

Please let us know the outcome after you’re repair.
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Old 10-21-2018, 09:00 PM   #5
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We had the same issue, opened the valve on the head when pumping out and it drained fully.
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Old 10-21-2018, 10:45 PM   #6
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Quote:
Originally Posted by Lollygag1 View Post
We had the same issue, opened the valve on the head when pumping out and it drained fully.

There's only reason why it should be necessary for the tank to pull in air through the toilet to be able to pump out: the tank vent is at least partially blocked (totally blocked and the pumpout wouldn't be able to remove more than a gallon--two at most--before the pump pulls a vacuum that won't allow it pull out any more).



I'm guessing that the slit or screen or whatever is in the vent thru-hull is clogged with dust, pollen, salt, or an insect. Try scraping it out to find out if that solves the problem.


If the vent IS completely blocked, using the toilet will pressurize the tank, which can result in some very unpleasant consequences, the least of which is a geyser when you open the deck pumpout fitting.



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Old 10-22-2018, 04:13 PM   #7
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I borrowed the attached file from the GB Owners forum. It was authored by Gordon Sivley. He owns a 1994 GB42 Classic.

I found Gordon’s paper addressed the problem the OP, Oldersalt, currently has on his GB32. I also am currently making repairs on my holding tank using the same “road map” that Gordon so carefully took the time to publish.

I thought the timing was too good to pass up and decided to present Gordon’s fix on Trawler Forum.

http://grandbanksowners.com/gbb/down...le.php?id=9885
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Old 10-22-2018, 04:34 PM   #8
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Old 10-22-2018, 04:40 PM   #9
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Oh! I’ll copy it as a .pdf file and repost it. Give me a few minutes. Thanks.
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Old 10-22-2018, 05:16 PM   #10
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Here you go...
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File Type: pdf Grand Banks Holding Tank Discharge Tube Replacement.pdf (300.6 KB, 248 views)
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Old 10-22-2018, 05:21 PM   #11
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Here you go...
Thanks for the heads up, Al! You saved me some time on an otherwise busy day.
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Old 10-22-2018, 05:35 PM   #12
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Thanks for the heads up, Al! You saved me some time on an otherwise busy day.
Get back to work and quit reading TF!
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Old 10-22-2018, 06:11 PM   #13
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Question

Gordon Seattle's description of how to replace the pickup tube on the holding tank is great, and probably applicable to many others besides Grand Banks. I have been assuming that since the tank on my GB 32 is hard plastic the interior parts of the tank would also be plastic. I will soon find out!

Also, trying to figure out how to handle the small (about 6-8 inch) clearance between the top of the tank and the underside of the deck, but one thing at a time I guess...

I promise to post the results of this little project on this forum and the GB owners forum.

Thanks everyone
Oldersalt
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Old 10-22-2018, 06:45 PM   #14
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Quote:
Originally Posted by Oldersalt View Post
Gordon Seattle's description of how to replace the pickup tube on the holding tank is great, and probably applicable to many others besides Grand Banks. I have been assuming that since the tank on my GB 32 is hard plastic the interior parts of the tank would also be plastic. I will soon find out!

Also, trying to figure out how to handle the small (about 6-8 inch) clearance between the top of the tank and the underside of the deck, but one thing at a time I guess...

I promise to post the results of this little project on this forum and the GB owners forum.

Thanks everyone
Oldersalt
My thought at the time, also! Found out they didn’t read Peggy’s book.
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Old 10-22-2018, 09:20 PM   #15
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If the vent IS completely blocked, using the toilet will pressurize the tank, which can result in some very unpleasant consequences, the least of which is a geyser when you open the deck pumpout fitting. --Peggie
And the worst of which is that the blocked vent decides to blow off the top of the holding tank. The geyser does not take place on deck. It takes place in your engine room and gives you 30 gallons of....stuff...geysered all over. Trust me on this. Bad pic but that was what was sticking in the top of the tank for a vent. Entirely blocked and rotted. It took DAYS of cleaning before I could get in there to take the picture. Peggy was my Mental Health Nurse for about 2 months after this occurred as it took weekly one on one counseling sessions to get the smell out.
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Old 10-22-2018, 11:00 PM   #16
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I can’t imagine how much fun that was...
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Old 10-22-2018, 11:34 PM   #17
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I can’t imagine how much fun that was...
We owned the boat for 1 week. A couple of days earlier we brought it up north to Stuart, FL from Ft. Lauderdale. Put her in a new slip and were meeting the previous owners that morning for a "show me how it works" day cruise. I over pumped the head and pressurized the holding tank thinking it was empty. It was not. Hey, did you know that my boat has a little gauge in the aft head that shows the current level of "stuff" in the holding tank? It read empty that morning. It read empty because, unbeknownst to me at the time, you have to pull a switch in the head to turn it on. I learned about that little silver pull switch when the previous owners arrived 5 minutes after Vesuvius let loose in the engine room.

The silver lining is that it will never, ever, EVER, get worse than that. Replace sanitation hose? Clear a clog? Please!
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Old 10-23-2018, 07:09 AM   #18
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Now I can guess at the origin of your boat's name......
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Old 10-23-2018, 07:13 AM   #19
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Should have gone with Brown Bilge Susan.

Actually "Black Eyed Susan" is the State Flower of Maryland. When talking to people from Maryland we are good to go. Not so much down here in Florida where folks always ask "Is Susan your wife?"
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Old 10-23-2018, 09:27 AM   #20
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Consider trying stopping pump out and briefly remove pump hose to let air into the tank then try resuming pump out. If a blocked vent is the issue pumping should resume. If it still does not resume that gives evidence that plugged vent is not the issue.
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