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Old 01-10-2020, 07:35 PM   #1
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Default Maxum 3000 SCR (2001) Black Waste Holding Tank Ė Smells, Removal, Hoses etc.

Does anyone know who made the holding tanks, what material they are made from, what to use to seal the 1-ĹĒ threaded Sierra plastic hose tail fittings and what the tank boss threads are i.e. BSP, NPT etc. (I suspect NPT as the tank is likely to be American made) ???

I keep getting holding tank smells in the boat. Itís been difficult to find out where the smell is coming from. Usually when we flush the manual Jabsco toilet this happens but there is always a residue smell and when at sea it can get worse. I suspected the vent but Iíve not been sure, no inline vent filter is fitted. Iíve checked the vent line, the hoses, macerator, and took a good look at the holding tank while in situ. All seems ok but Iím not 100% sure. The last straw was when we had the boat out in rough seas recently and the smell in the helm / aft seating area was just horrid. So, I decided I need to take the holding tank out and check for cracks etc. Not a nice job with some residue leakage but I got the tank out in an hour or so. Once flushed, bleached and flushed several times I plugged the holes and put a small compressed air pressure test onto the tank. Using a proprietary leak detector fluid I found no leaks so Iím kind of at a loss. The tank, now dry, really smells, the smell is from the inside. Although itís pretty clean internally there is residue white stuff some flaky looking and some fatty looking in places attached to the inner upper side walls.

Iíve been reading about the possible need to change the hoses due to leaching the foul water, they are 19 years old but look ok!. Incidentally the pump out and vacuum out hoses enters the tank at the bottom, so they are constantly flooded in foul water at their low point, this is the design. A dip tube would have been a better idea but we have what we have. Iím going to do a damp hot towel test on the hoses to see if they are leaching, and if they are I will replace the hoses. The only other options, as far as I can make out, is to fit an inline vent filter and or have a new tank made.

The plugs I bought for blanking the tank were 1-1/2Ē BSP, not thinking about the tank being American. When I went to fit them they kept wanting to go in skew whiff which makes me think the tank bosses are NPT, does anyone know for sure if this is the case.

Finally, I need to reseal the hose tail threads back into the threaded bosses which are welded to the tank. Iím not sure what sealant to use here. Iíve spoken to Sika Sealants and they havenít got anything which will bond PVC-u to polypropylene. They say that you canít bond to polypropylene. Now Iím guessing the blue Sierra hose tail fittings are made from PVC-u and that the holding tank is made from Polypropylene. Does anyone know for sure if this is the case or otherwise, and does anyone have any sealing suggestions other than PTFE tape.

For interest Iíll try and post some pictures of the tank in question. Thanks.
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Old 01-10-2020, 10:05 PM   #2
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I've never heard of polypropylene ever being used for marine water/waste tanks. They've always been roto-molded from LDPE. I was in the plastics industry (Union Carbide and Rubbermaid Commercial Products for nearly 30 years) and am very familiar with all plastics.


Here's a suggestion - Google this - "how long do hoses last on a marine waste tank" for some great information. You'll learn that your hoses perform well up to 5 years, then start to degrade allowing odours.
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Old 01-11-2020, 02:00 PM   #3
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Replacing hoses will make a big difference.
I also have to ask how you're treating the waste? There are many posts on the web about different approaches, but they all are correct in that containing smells starts with proper treatment of the waste. I still use the blue RV additive and the waste only has almost no odor when the pump out cap is opened.

IMHO, this is the only way to truly address the odor. Containment (inline filters, etc) only try to block smell from leaving the tank.
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Old 01-11-2020, 08:41 PM   #4
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If you get the smell when you flush it could be a clogged vent.
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Old 01-13-2020, 02:48 PM   #5
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I've used teflon tape to seal the threads. I've never had any issue with leakage. The hoses are the issue, not the fittings or the tank unless the fitting or tank is cracked. Even the very best hose won't last more than 10 years.
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Old 01-14-2020, 09:29 PM   #6
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Gents, thanks for the replies so far. I've managed to find a few things out. As Jimq26 says, the tank is likely to be made from Polyethylene. I have found some manufacturers on the web who make waste tanks form Polypropylene but they are few and far between with Polyethylene seeming to be the makers choice. The blue hose tail fittings are branded Sierra and made from glass reinforced Nylon. They are 1-1/2" NPT and 1/2" NPT not BSP which makes sense as they are American. I've been told Bainbridge in the UK are a supplier / distributor of Sierra fittings, I've to ring them in the morning, we'll see! I don't really want to use Teflon or PTFE tape but to keep the thread sealing sealant as original so Ill keep looking into this. Thanks for all the advice on changing the hoses. I've read up a lot about it and yes the hoses need changing so thanks again. Any other comments or suggestions most welcome. Thanks
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Old 01-15-2020, 01:53 PM   #7
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Quote:
Originally Posted by darren uk View Post
I don't really want to use Teflon or PTFE tape but to keep the thread sealing sealant as original so Ill keep looking into this.
Here is a quote from Peggy Hall, who is a well respected professional in marine plumbing and sanitation and has published several books on the subject. This has been quoted from a sister site:

Quote:
Originally Posted by peghall View Post
Welcome aboard Kupe! Teflon tape is the ONLY thing to use. Tank fittings are NPT standard, which is slightly tapered--so slightly that it's impossible to see the taper in a "pipe" that short...so you need to be be careful not to OVERtighten hose fittings. That will result in a cracked female fitting, if not immediately within a short time. A maximum of one full turn past hand tight plus enough to aim an elbow where it needs to go is all you need. If it leaks, use more tape.
http://www.cruisersforum.com/forums/...eply&p=2634544
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