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.
Thanks
Oldersalt

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.

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.

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.

We had the same issue, opened the valve on the head when pumping out and it drained fully.

Lollygag1 said:

We had the same issue, opened the valve on the head when pumping out and it drained fully.

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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.



--Peggie

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/download/file.php?id=9885

Must be a member to see it

Oh! I’ll copy it as a .pdf file and repost it. Give me a few minutes. Thanks.

Here you go...

FlyWright said:

Here you go...

Click to expand...

Thanks for the heads up, Al! You saved me some time on an otherwise busy day.

Giggitoni said:

Thanks for the heads up, Al! You saved me some time on an otherwise busy day.

Click to expand...

Get back to work and quit reading TF!

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

Oldersalt said:

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

Click to expand...

My thought at the time, also! Found out they didn’t read Peggy’s book.

HeadMistress said:

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

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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.

I can’t imagine how much fun that was...

Comodave said:

I can’t imagine how much fun that was...

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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!

1st Base
Now I can guess at the origin of your boat's name......

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?"

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.

Bayview, a word of caution on that test. When our boat was relatively new to us , I was "sprayed" when disconnecting the pump out hose. I had pulled a vacuum in the tank due to a blocked vent . When I disconnected the hose the inrushing air forced a fountain of goo all over the side of the boat, and me. No joy that day.
Friends and family with us that day were calling me 'Captain Crap'. Try to get help hosing myself down was futile, as they were all running away.

Bill

I'm so paranoid I use a small canvas drop cloth to circle around and cover the holding tank cap if I do anything with it. Uh huh. Not going there. Paranoid. Crap kills. Captain Lives Matter.

bayview said:

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.

Click to expand...

That won't help much because the tank vents above the surface of the contents, providing air to replace contents as they're pulled out. The pumpout pulls from the bottom of the tank, so opening the pumpout cap only relieves pressure, it doesn't provide even a temporary source of air. All it would do is allow the pumpout to pull out another gallon or two before it pulls a vacuum again.


--Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein

I would be willing to bet that most any boat with some age has a clogged or partially clogged vent. Either from critters building nests from the outside or from a once overfilled tank causing stuff to be forced into the vent line. Always worth a check.

I would be willing to bet that most any boat with some age has a clogged or partially clogged vent.

Only those with owners who routinely overfill the tank and/or fail to realize that tank vents, like everything else on a boat, require a some maintenance...which can be very easy:

Replace the "vent" thru-hull (which is actually designed to keep sea water out of fuel and fresh water tanks and should never have been used to vent waste tanks) with an open "bulkhead" or "mushroom" thru-hull that you can stick a hose nozzle against and backflush the vent line every time you wash the boat and/or pump out. Better yet, increase the vent to at least 1"...easy to do on most boats thanks to a li'l gizmo called that Uniseal UNISEAL .

Be sure to check for mud dauber nests in all your tank vents each spring and scrape 'em out before backflush it. Anything else that's tried to set up housekeeping in it will just get a water slide ride into the tank. A larger diameter vent and open thru-hull will also increase the free exchange of oxygen with the gasses in the tank that's needed to create the aerobic environment needed to prevent holding tank odors.


Unfortunately a filter in the vent line makes backflushing it impossible because filters become "toast" if they get wet. However, increasing the ventilation to provide the oxygen needed should eliminate the need for a filter.

Even in the absence of vent maintenance, geysers out the pumpout cap are avoidable if you pay attention to the indications that the vent is blocked and cease use of the toilet till you can clear it: a manual toilet that's becoming increasing harder to pump...any toilet that begins to "burp" and "spit up" flushes. I can't count the number of people who've spent hours and money trying to clear a clog in the plumbing when the problem is actually a blocked vent that's pressurized the tank.

--Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein

Let's just assume that when we buy a 20-30-40 yr old boat that it's prudent to rip it out all out and start over - ie, toilets, hoses and holding tanks I'll be starting on that adventure soon.

And my son that was recently badly injured in a 4-wheeler/atv accident may indeed be helping me - praises indeed He will be having plastic surgery Fri to mend fractured bones in his face - eye socket and skull over his eye. Miraculously his eyes are ok and to look at him he is as handsome as ever - 16 broken bones and no stitches or cuts. And the brain injury is mainly contusions that will take 3-9 months to fully heal - to the extant they will. I watched him talk to two high school friends for an hour this morning - amazing to see - considering two weeks ago we almost lost him.

Greetings,
Mr. FC. Good to hear. You never stop thinking about your kids and THEIR kids no matter how old you or they get.

FoxtrotCharlie said:

Let's just assume that when we buy a 20-30-40 yr old boat that it's prudent to rip it out all out and start over - ie, toilets, hoses and holding tanks I'll be starting on that adventure soon.

And my son that was recently badly injured in a 4-wheeler/atv accident may indeed be helping me - praises indeed He will be having plastic surgery Fri to mend fractured bones in his face - eye socket and skull over his eye. Miraculously his eyes are ok and to look at him he is as handsome as ever - 16 broken bones and no stitches or cuts. And the brain injury is mainly contusions that will take 3-9 months to fully heal - to the extant they will. I watched him talk to two high school friends for an hour this morning - amazing to see - considering two weeks ago we almost lost him.

Click to expand...

Best news I’ve heard all day ?!

That truly is wonderful news. I hope he continues to heal and quickly gets back to normal health and strength.

At the risk of starting a s#it storm I must share what my doctor daughter told me when she was a young intern in the emergency room at a Tennessee hospital. After her first day I asked her what she learned. She said "Never, ever, get on an ATV or a motorcycle." Hopefully someone or someone's kids will listen.

FC, Having recently gone through something similar with family, I understand how far he's come. What a blessing! I have a strong feeling that his future improvements will be even more amazing!

Great to hear he's well on his road to recovery. Wonderful news.

Cheers!