Holding Tank won't rinse thru deck plate

[nzjnyf]

Hello, I'm new to the forum and relatively new to boating. In the fall, I purchased a 2001 Four Winns 280 horizon. So as one of my fall duties, I went to the marina to pump out the holding tank. A few gallons were removed and the dock hand attempted to rinse the tank through the deck plate, but it would only take a small amount and would never drain back into the tank. I attempted to snake the line through the deck plate and it still wouldn't drain. So I'm guessing there might be an issue with the vent. Before I try to run some liquid through the vent, I wanted to make sure I wasn't going to do any damage? I don't know if there is a filter or if it matters if it is a Vacuflush system? If you look at the picture, what is the device that the vent line connects to? Should I remove the vent hose from the tank? Does anyone have any suggestions?

[JoeRobertJr]

Hopefully, someone can help...

[peghall]

I see you've just joined us today...welcome aboard!

To start with...It appears that your VacuFlush system is a VHT (vacuum holding tank) system in which the holding tank also doubles as the vacuum tank.VHT 4500 / VHT 12 You'll find the owners manual for it here Dometic/SeaLand VHT owners manual.pdf That gizmo in your photo appears to be part # 16 in the exploded drawing Dometic 4501-4502 VHT Parts Diagram

Your description "able to pull out a few gallons, then nothing more" is almost a textbook example of a blocked tank vent. Tank vents--all tank vents, not just holding tank vents--have two primary functions: to provide an escape for air displaced by incoming contents and to provide a source of air to replace contents as they're drawn out. If no air can escape, the tank can become pressurized...if no air can be pulled in, the pump pulls a vacuum that won't let it pull any more out.

But that doesn't apply to your system...It doesn't vent the same way every other tank does...there's only a "pressure relief valve" that prevents the tank from pressurizing and SHOULD also open to allow pumpout. That part seems to have failed. You need to call Dometic/SeaLand tech support...they're in Ohio: 800-321-9886

--Peggie

[nzjnyf]

Thank you Peggie! I called the support number you provided and was redirected to regional support. The guy I spoke with said there is a known issue with a duckbill valve in the diptube that has a history of getting inverted. He asked me to send him a photo, and to attempt to continue use of the toilet and try to pump it out. If it works, it works, don't worry about it. If not, I may need to replace that valve?

[peghall]

I'll let the regional tech support guy tell you how to do that if it becomes necessary. But I'll be glad to help you learn how to use and maintain your toilet to keep it trouble free...the VacuFlush is a bit different from other systems.
--Peggie

[GordMay]

Greetings and welcome aboard the CF, nzjnyf.

[roland stockham]

If you are new to boats you may also be new to septic tanks of any sort. So couple of basic pieces of advice. Bathroom tissue is a common culprit of blocked anything. When wet it can form solid clumps (ever make paper mache at school?) Not to be sexist but if you have ladies on board this is much worse, they use more paper. The solution is very expensive biodegradable paper made for RV's etc or a sani-bin for paper. The rule is 'nothing down the pan that you did not eat'. The second issue is sludge formation. If the contents are to dry they can set, particularly if left with little movement for a while as they are in a marina. The cure for this is adding enough liquid, don't try to restrict flushing to save filling the tanks. Also regular emptying. If they system is not going to be used for a while (more than a couple of weeks) empty and flush. Finally sail regularly, the motion churns everything up and keeps it free flowing!

[peghall]

The solution is very expensive biodegradable paper made for RV's etc or a sani-bin for paper.

Those aren't the only solutions. "Marine/RV" toilet paper is just cheap flimsy TP repackaged for a highly inflated price. There's a very simple test to determine whether any TP is suitable for use in a marine toilet: tear off a couple of sheets and put 'em in a glass or a mason jar full of water. Come back in an hour or two and stir or shake the glass/jar. If the wateris "milky" and all you see is "snow," it's fine for use aboard. But if the sheets are still intact or mostly intact, try another brand. Fwiw, Scott Tissue has an institutional TP that a lot of boat owners are using aboard successfully. Available from Sams and Costco.


--Peggie

[senormechanico]

There are lots of youtube videos comparing RV paper to Charmin etc.
We've used Charmin on the boat for several years without a problem.

[mitiempo]

Your vent hose rises and then dips creating in effect a "P" trap for water (or waste) to accumulate. A vent should rise continuously without any dips.

[peghall]

If you read post #3 in this thread, you'll learn that his is not a "normal" system.


--Peggie