Home » Public Forums » GMCnet » Black Tank Replacement Questions (DIY black tank replacement)
| Black Tank Replacement Questions [message #344711] |
Mon, 01 July 2019 10:58  |
Stu Rasmussen
Messages: 130
Registered: January 2019
Location: Silverton, OR
Karma: 0
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My newly acquired '77 Birchaven came came equipped with a VERY large hole in the black tank where the outlet fitting used to be. (As a side note, both the rear bath units I looked at had similar black tank problems - is this a known design anomaly?)
First question: is Jim's GMC-4 tank the correct one for my coach? https://www.gmcrvparts.com/product-p/gm23-23.110.5.4.htm
Second question: If that is the correct tank, does it come as pictured without holes for the toilet and vent connections - i.e. do I drill them myself?
Third question: Is this replacement tank ABS material or is it something else that needs a special cement for making connections to the tank?
Fourth question: While I am replacing the tank would it be worthwhile to install some sort of flushing mechanism (like https://www.gmcrvparts.com/product-p/gmrv11-0348.htm ) instead of relying on the 'hose and nozzle down the toilet' ritual?
Thanks in advance for any advice.
Stu
Stu Rasmussen W7QJ
Silverton, OR
'77 Birchaven
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| Re: Black Tank Replacement Questions [message #344714 is a reply to message #344711] |
Mon, 01 July 2019 12:12  |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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Stu-
you will have to call up Jim K, and get the specifics on the tank he is selling. I am not familiar with the rear bath birchhavens, but the proper tank on other models can be found and they are just bolt in.
as far as material, I have no idea, and have seen arguments from people saying it is abs, or polyetholine, or whatever other plastic. You will have to verify that question.
Now that I have not answered those questions, let me state a few things I think that should help:
you want some isolation, so I would not glue any fittings that you can use a rubber collar on. vibration will take out glued pipes if everything is solid mounted to each other. So on the 3" outlet on the tank, use a 3" rubber coupler to go to the rest of the drain plumbing.
The tank should be mounted to the body(usually the toilet flange is a solid mount to the floor, and solid to the tank), but should not be mounted solid to the frame.
some may argue, but the installation of a "macerator" is a key item for our GMC's. very clean, no need to store or clean out a hose, and when you are so low to the ground as the GMC is, no bending down, reaching under the coach, and some dump stations are higher, so makes dumping a breeze. I have about a 10' hose that is easily pulled out, I pull a valve, and hit the switch. it pumps out in just a few minutes. turn off the switch, it the valve and carefully rinse the end of hose and put cap back in, and the hose goes back into the holder.
I just ordered this macerator today:
https://www.amazon.com/gp/product/B000O8F9BI/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
here is when I installed it back in 2011:
http://lqqkatjon.blogspot.com/2011/08/macerator-install.html?m=1
So It has been pumping reliably for 8 years. It failed me yesterday, but it might just be a bad ground or??? for $120, it is a part I rely on, so it is getting replaced on Wednesday. If I am going to crawl under to deal with it now, I don't plan on dealing with it for another 8 years.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: Black Tank Replacement Questions [message #344716 is a reply to message #344714] |
Mon, 01 July 2019 12:37 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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lqqkatjon wrote on Mon, 01 July 2019 13:12Stu- <SNIP>
some may argue, but the installation of a "macerator" is a key item for our GMC's. very clean, no need to store or clean out a hose, and when you are so low to the ground as the GMC is, no bending down, reaching under the coach, and some dump stations are higher, so makes dumping a breeze. I have about a 10' hose that is easily pulled out, I pull a valve, and hit the switch. it pumps out in just a few minutes. turn off the switch, it the valve and carefully rinse the end of hose and put cap back in, and the hose goes back into the holder.
I just ordered this macerator today:
https://www.amazon.com/gp/product/B000O8F9BI/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
here is when I installed it back in 2011:
http://lqqkatjon.blogspot.com/2011/08/macerator-install.html?m=1
So It has been pumping reliably for 8 years. It failed me yesterday, but it might just be a bad ground or??? for $120, it is a part I rely on, so it is getting replaced on Wednesday. If I am going to crawl under to deal with it now, I don't plan on dealing with it for another 8 years.
Stu,
What Jon did not include was:
Do not install a macerator without a valve, as the machine will leak sooner or later.
Do not eliminate the capability to gravity dump when you install a macerator. Sooner or later (just like Jon and so many others), you will have to service the macerator with the black tank full.
If you install a macerator, have adequate electric supply to it. They draw 15+ amps. That is #10 if you connect to the house battery in the rear.
Caveat: I do not own a macerator. I have installed and serviced more than a few.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Black Tank Replacement Questions [message #344719 is a reply to message #344714] |
Mon, 01 July 2019 13:09 |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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Senior Member |
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lqqkatjon wrote on Mon, 01 July 2019 12:12
I just ordered this macerator today:
https://www.amazon.com/gp/product/B000O8F9BI/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
here is when I installed it back in 2011:
http://lqqkatjon.blogspot.com/2011/08/macerator-install.html?m=1
So It has been pumping reliably for 8 years. It failed me yesterday, but it might just be a bad ground or??? for $120, it is a part I rely on, so it is getting replaced on Wednesday. If I am going to crawl under to deal with it now, I don't plan on dealing with it for another 8 years.
With the above In mind, Read down a little further for this comment. You may not need to replace the macerator, just put in a little thicker gasket. JWIT
Bought this pump one year ago to keep as a backup, been sitting on a shelf since then. Got it out today (installed one is leaking) and noticed one of the SS nuts was loose. Turns out the brass bolt holding the hose input to the impeller housing is broken (see image). I have had this happen to three other units installed in my boat over the past 3 years but figured it was due to mechanical forces during use. Either I was sent a used unit (it looked and smelled clean and new, including silicone still seen on the metal washer) or the bolt simply failed while sitting on the shelf. If you buy (or own) this unit, get yourself a tap and die set with a #10-32 die and some 3/16" rod so you can make yourself some new ones when they break. Also, if you have trouble with blowing fuses due to resistance of the impeller turning, replace the thin paper gasket with one slightly thicker (removes pressure from the impeller): Remove existing gasket, trace with pen, cut new one with x-acto blade, optionally coat with liquid gasket during install. When the bolts aren't broken and the gasket isn't too thin, this unit works fine... Low expectations keeps you smiling...
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
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| Re: Black Tank Replacement Questions [message #344722 is a reply to message #344719] |
Mon, 01 July 2019 13:28 |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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I think my failure has to do with where mine is mounted. it gets it's share of road spray, and I think it gets some snow/ice on it as well, just from where it is parked. I should also update my current mounting of the macerator is actually a little higher. I did pull it once, flip the pump head, so the feet could be facing upwards. That gave me some more clearance to the ground. It would actually be best to move that pump back towards the front a little bit, but when I first installed it with my old tank, that was not working well. With a new tank, I can see how it could go back more to be protected. My macerator in it's early years before I moved it up an inch higher, was tore off twice. Once when the wife was backed up a steep crappy campsite. and a second time when I misjudged an alleyway incline and my bags were probably a little down that day too.
so the past 8 years has been a rough 8 years for that pump. And the pump might be fine. The only troubleshooting I did yesterday was to check for 12.x volts leaving my switch that goes to the pump. I am just using a 30 amp rated switch that comes off a circuit breaker fed by the house batteries. either 12 or 10awg wire, but it is a 2 or 3' wire. I also have girls with long hair, so 8 years of showering those kits might be wrapped up in that pump too.
Matt is right about the valves and the 3" dump. Always nice to have fail-safes. But you want to move your valves a couple times a year. I have seen many rods come out of old valves that have never been open for years. I know mine all get operated when I winterize/summerize.
Another thing on the macerator, I kept a 1" discharge hose. I know many people pumping a 3/4" discharge hose. both work and I have seen others that have been using a 3/4" hose for decades, but I personally think pumping through a 1" hose is faster and easier for the macerator.
Stu-
as far as flushing out the tank. I think just good tank maintenance. a flushing system is good only if it works and does not cause more things to leak later. I personally skip any flushing system. fill up and rinse the tank. I think water sloshing around while driving does the best job of cleaning things. I am fortunate to have a dump station near my house, so I always dump after driving a while. Use lots of water and have had no problems.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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