2004 420 Passage aft black water tank won't pump out

Fgard

.
Mar 18, 2018
8
Hunter 420 Passage Gulfport
I've flushed the vent line with water and it is not plugged. I'm moored in Boot Key Harbor and the pump out guy says he's getting no suction/vacuum hissing when he puts the pump out hose in the pump out deck plate. He said to check waste hose connections. Connection at deck plate is good but I can't figure out how to get to the fitting on tank under aft bunk. Anyone know?
 
Dec 2, 1997
8,709
- - LIttle Rock
No suction at all tends to rule out a blocked vent, but I'm not 100% convinced it isn't. At least 90% of vent line blockages occur in two places: the vent thru-hull and at the tank--that end of the hose and the vent fitting on the tank. So you can't be sure your vent is open until you've checked and cleaned out both.
If the problem is a loose waste hose connection, there'd be hissing at that location, plus flushing the toilet would push enough out of a loose connection to at least create some dampness around it. So I'm more inclined to suspect blockage in the discharge line, most likely in the tank at the fitting. Have you had any landlubber guests who might have disregarded your instructions NOT flush wet wipes? If so, that would be the culprit...and one of the few, if not the only, thing that a strong dose of something like Sew Clean can't dissolve. Is there an inspection port in the top of the tank? Sew Clean should dissolve any clog that's actually in the pumpout line.
An off-the-wall thought: is there ANY chance that the pumpout guy "plugged in" to the wrong thru-hull?
--Peggie
 
  • Like
Likes: Dave Groshong
Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
Did you blow into the deck fitting with a small shop vac? I had the wet-wipes blocking my tank exit. A blow sent the wipes into suspension in the liquid, and it all pumped out.
 
  • Like
Likes: Dave Groshong
Jun 26, 2009
19
Hunter 420 Olympia WA
On my 420 the tank is under the aft bunk, port side, forward, near the through hull fittings. I just changed out my tank sending unit. You can inspect a little through the hole. The vent is on top of the tank.
 
  • Like
Likes: Dave Groshong

Fgard

.
Mar 18, 2018
8
Hunter 420 Passage Gulfport
20190411_202233.jpg
20190411_202054.jpg
Thank you for the reply! I'm baffled. I can only see the 1.5 inch hose going into the top of the tank from the y valve and the 1.5 inch hose going into the bottom from the macerator. I can not see the vent or 1.5 inch hose to the deck plate - or any way to take apart the bunk covering the tank.
 

Fgard

.
Mar 18, 2018
8
Hunter 420 Passage Gulfport
Thank you for the reply, but the pump out guy assured me that if it were simply blocked, he would get hissing at the pumpout plate when he cracked it open after inserting it. My shopvac only vacuums so I'll try a plunger tomorrow.
 
Dec 2, 1997
8,709
- - LIttle Rock
Thank you for the reply, but the pump out guy assured me that if it were simply blocked, he would get hissing at the pumpout plate when he cracked it open after inserting it.
I'm assuming he's referring to the tank vent... Not always...that only happens if the tank is slightly pressurized. If it's seriously pressurized, he wouldn't get just hissing, he'd get a geyser. But if the toilet hasn't been used for several days, pressure in the system will dissipate via the toilet. Not much to start with, none left by the time he gets there.
Even if there's no longer any pressure in the tank, hissing in the toilet during pumpout is a big clue that the tank vent is blocked....that the pumpout is trying to pull in air from any source it can find. If there's no hissing in the toilet either, that supports my suspicion that something is blocking the tank discharge fitting or line.
--Peggie
 

Fgard

.
Mar 18, 2018
8
Hunter 420 Passage Gulfport
Before I try plunging or snaking, I'd really like to check the fitting where the pump out 1.5 inch hose goes into the tank but see no way to access it. Anyone ever been able to see that on a 420 passage?
 
Dec 2, 1997
8,709
- - LIttle Rock
Unless your pumpout line is really short I don't think a plunger would do much good unless the person plunging can generate a LOT of force. But a snake is worth trying. Unless your pumpout line is excessively long and has major bends in it, it should go all the way into the tank...or until it runs into a blockage--which it has a good chance of clearing.

--Peggie
 
Jan 12, 2011
930
Hunter 410 full time cruiser
Before I try plunging or snaking, I'd really like to check the fitting where the pump out 1.5 inch hose goes into the tank but see no way to access it. Anyone ever been able to see that on a 420 passage?
Most likely if it's like on my 410 you have to move the mattress and the then unscrew and remove the board above the tank.
 
  • Like
Likes: DayDream2

eianm

.
Jul 7, 2010
517
Hunter 42 Sydney
One other possibility is what i found with EXACTLY the same problem- I had a series of pin holes in my aluminum ezel tank!
 

Twille

.
Oct 8, 2012
63
Hunter 38 Henderson, nc
Just a thought the Vac hose from your shop vac should plug into the out side of the Shop vac motor giving you a blower instead of the normal “sucker”.