A Glimpse At The RV Underworld, Black Tank Tales

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February 11, 2010


The Lug_Nut View.  Beneath the modern glitter and shine of all RV’s is the underworld, the basement, and of course, the waste tanks.  Seemingly unchanged over the years, the black and grey tanks are filled and must be emptied as needed.  This, in most cases, is being done using the big stinky slinky, at least until now.  But, a new method using a smaller hose and a macerator is quickly becoming popular.  This new system has some advantages over the tried and true gravity drain method.  Let’s look at what it offers.

  • Can pump through a garden hose over a greater distance.
  • Propels the waste instead of relying on gravity only.
  • Tanks can be emptied at home by routing a hose through a bathroom window in the house.
  • Quicker to hook up once in camp.
  • Uses less water to flush after use.

However, along with the advantages it provides, it may have a dark side.  The macerator is made up of a small stainless steel impeller, similar to that of a blender.  The spinning blades of the impeller puree any solids instantly on contact.  Following the emptying of the black tank, the grey tank is emptied.  While generally there are no solids found in the grey tank, there are hairs.  This hair, unlike paper and solids, does not all pass through the macerator, instead it may become wound into the impeller shaft.  Over time, if not cleaned out, the hair may build up and start binding the macerator’s movement.  So, and this is the dark side, it may one day need to be dismantled and cleaned.  Now, I don’t mind opening a pump and cleaning it, but a black water sewage pump?  Yuk!

Now, here’s a Black Tank Tale that actually happened and it involves a macerator pump.

A couple, we will call them Paulo and Jillian, owned a very luxurious coach.  This coach boasted of all the latest bells and whistles, including a macerator sewage system.  During a stay at an RV super show they had the need to dump their tanks.  Upon inserting the slim hose into the dump, Paulo switched on the macerator.  A clatter like that of a bag of ball bearings in a squirrel fan could be heard coming from the small disc like pump.  What could it be?  Was the pump self destructing?   Grrrrrrrr……….

Paulo contacted the coach maker to advise them of his plight and inquired as to what it might be.  The technical service people were stumped and could not imagine what would cause such a sound, but would work on it and get back to him.

They managed to empty the tanks and headed to their next stop, to meet friends at an RV resort three hours to the south.  Upon arriving at their destination, acquiring a site and getting set up, they saw a repair service truck parked just across the road.  Though the service vehicle appeared more like a derelict laundry truck, the words “RV Repair” was prominently displayed on the side.  Paulo approached the truck to see if they could check out and repair his macerator.  The man inside the truck stepped out and gave Paulo a toothless grin “Yeh, we’re real good at stuff like that.”  With that, the man, followed closely by two others, headed for their coach.  Visions of the Three Stooges ran through Paulo’s mind as they introduced themselves to him.  But only the first one had a Stooge name, Larry.  Apparently they were all brothers.  The others were Daryl and I think the third was also called Daryl.  Anyway, they swarmed around the problem area and discussed a strategy.  Paulo and Jillian left them to do their thing and walked up several sites to a friend’s coach to enjoy a home made chili lunch.  This guy makes the best chili this side of the free world.  Supposedly the secret is to count the exact number of beans to put in.  For this reason it is believed he got the name, The Bean Counter.

An hour later Paulo decided he had better go back down and see how the mountain boys were making out on his issue. He was gone for sometime then appeared back at the Bean Counter’s site, a piece of paper towel in his hand.  “Check this out!” he said opening the folded paper towel.  A small light brown stone lay in the paper.  “There was at least a dozen of these in the macerator, even bent the blades.”  He continued “What could this be?  Daryl, or maybe it was Daryl, tried to crush it with pliers, but it was indestructible. Maybe it’s from another planet or something.”

cherry2After some thought and a brief silence Jillian exclaimed “Cherry pits!  It’s cherry stones!”  All soon agreed, it was indeed a cherry pit.  But, how did cherry pits find there way into the waste tanks?

Jillian again spoke. “Cherries!  We ate all those cherries last week.  Paulo, what did you do with your pits?”

“I threw them in the garbage.” He said defensively.  They again fell silent.  Paulo and the others slowly all turned to Jillian.

“What?” she said.  “Don’t look at me.  I swallowed all the pits of the ones I ate!”   It took several seconds before Jillian realized what she said, and what had transpired.


Well, no damage.  The stainless cutter blades were bent back into their original shape and the macerator again purred while churning out a continue stream of liquid.  Paulo has convinced Jillian, for the sake of the macerator, not to swallow anymore fruit pits and was happy this was identified prior to peach season.

Fortunately, having the macerator option does not preclude you from having the large conventional sewer hose, which, apparently, is good to use during the fruit harvesting time.

Life Can Be The Pits    –     Lug_Nut     –     Peter Mercer

NOTE: To avoid embarrassment the names were cleverly altered as was the location and timeframe. Since the incident both Paulo and Jillian were relocated by the Nitwit Protection Program.  Jillian has devoted her life to teaching third world children how to make beaded necklaces using cherry stones.  Paulo has developed a designer macerator pump.  It has the logo of your favorite team on it as well as a cherry stone warning and disclaimer.


Leave a Reply


  1. Rhonda Mapua

    I precisely wished to thank you so much yet again. I do not know the things that I would have handled without the type of methods contributed by you regarding my area of interest. This was a very distressing problem for me, however , encountering the expert style you handled it made me to jump over happiness. I am grateful for your guidance and thus sincerely hope you know what a great job you were accomplishing instructing men and women thru your websites. Probably you haven’t got to know all of us.

  2. Bernie & Karen

    We’ve been using a macerator since Jan, 2010. Thought all was fine until I decided to change my waste valves… OMG, there was “sludge” everywhere – inside, downstream & upstream of the waste valves on both gray & black tanks. I just don’t think it has the flow to get all the crude out. Slow buildup over time and it was getting really stinky too!

  3. ChuckL

    I have a suggestion for the problem of cleaning the hair balls from a macerator pump without, or at least with a greatly reduced the danger of infection. After dumping and when you intend to clean the hair balls, set up a recirculating system with a chlorine bleach concentration for several minutes.

    This should only recirculate through the pump to prevent the chlorine from destroying your treatment chemicals.

    You could also set up a servicing station in you garage and just plug the macerator pump into this. You may also be able to simply submerge the pump, but not the motor, into a bucket of the bleach solution.

    Happy touring.

  4. Lug_Nut

    John, Great idea. I will pass it along to Jillian. Thanks for the comment.

  5. John

    Skip the electric macerator, get a Sewer Solution. It’ll handle cherry pits with no problem. Way cheaper too.

  6. John

    Hi Lug_Nut,
    A very funny & informative story. Always good to have the old 3 inch backup
    just in case. Guess like anything else, it has its’ pros and cons.
    Seems like a lot of people like them despite potential problems.
    Why don’t they make cast impeller bodies? Seems logical they will last a lot longer.
    I think if I had a problem impeller, I would mail it back to the factory, as is.


  7. Chuck S

    Stew RV
    I guess my question is; why wasn’t the unit properly serviced and checked out before delivery?? But, I’ll bet that had to be one heck of an embarrassing mess, and costly cleanup, yucky pooh.

    I had a hand back me into a spot and ran into a rock that turned up by a tire, it knocked a hole in the tank and we didn’t find it till the next morning, not only a mess to clean up, but a real pain to repair. Luckily we had emptied the tank on the way to the park.

  8. Lug_Nut

    jerry, Yes, you would not expect that someone would eat something that would not go through a macerator. Thanks for the input.

  9. Lug_Nut

    StewsRV, Yuk! I suppose that happens more often than we think. Thank you for that with us.

  10. jerry

    The old boat addage of “please don’t put anything in the head that you haven’t eaten first ” falls kinda moot at this point, doesn’t it. Fortunately boaters are not allowed to use macerators on inland waters. No overboard dumping………………..See ya!

  11. mrt_whit

    great story, hahaha

  12. Sue Damaske

    Does anyone know what the DOT requirements are?

  13. John

    I bought a macerator at my local RV dealership. I forgot the product’s name, but here are the features I LOVE
    1. It is powered by water, not electricity.

    2. It has a lever that points the water flow UP when you are almost finished, to rinse out the bottom of the drain valve (I use my built in hose connection to rinse the tank itself from the top).

    3. It operates quickly (I do not let my black water tank get full before I empty it – there are still some state rest areas that have not closed their tanks, and Flying J [and perhaps other] truck stops have free dumps, so I am not carrying around all that weight)

    4. It has a shut off valve, so I do not have to disconnect it to comply with DOT requirements. I just curl it up in the compartment when finished dumping.

    5. The macerator cleans up nicely, so if I have to take it apart, it should not be a stinky job.

  14. 2009 Admiral

    My new motorhome came with a macerator pump. I found two problems. First I got tired of taking 25-30 minutes to empty two 55 gallon tanks and enduring the scorn of the others waiting for the dump station. Second, because of the slow flow I ended up with mounds of solids that took a lot of work to get rid of. I still keep it in a compartment however, in case I ever do need to pump uphill or a long ways.

  15. Rich Oliveria

    I think I may get one of those macerator thingys. Then I would only have to carry one hose instead of one for the Black water and one for fresh……

  16. Ian McKee

    I have a 37′ fifth wheel with both a macerator and a conventional dump valve. I use both depending on the situation and , with 75 gallon black a gray tanks, .have no problem with the macerator. I did drop a fork into the black tank when dumping some dishwater and stopped using it for a long time worrying about it going into the blades. It never came out the conventional sewer dump so this summer I went back to the macerator and, so far so good. At least, if it does mess up the macerator I have an alternate way to go.

  17. Jim

    i wish they would put a real motor on these pumps
    the brushes are in plastic retainers and the motor gets hot and melts the brush glides .
    no one wants to mess with nasty pump housing
    don;t put wipes through these pumps

  18. Ken Saccocia

    I’ll bet Jillian was a BLOND.

  19. Ronald

    We bought our first rv in Oct. ’04. We attended The Rally in Redmond OR in ’05 where I found a macerator system to empty tanks. Jumped right on it and still think its the best add-on we’ve gotten. Sure don’t miss dragging out the sewer hose, hooking it up, rinsing it out and stuffing it back in again!

    No pits here!

  20. Mike Turner

    There is another dark side to macerators. And one that affects every tank they are used on. They simply do not have the flow the large hose has. We have several years of macerator esperience and know this well.

    Using a macerator, the fluid flows so slowly that little turbulence in the tank occurs, but settling does. Thus one can (using a transparent elbow) watch dark fluid flow for a very long time while flushing the tank clean. With the three inch hose and free flow, it only takes a few minutes to get clear water coming out of the black tank. We no longer use a macerator unless it is the only practical option (such as at home), and when we have time to kill.

  21. Barry Engleman

    I remember an old Chicago’s song – “What goes up, must come down”. This is very similar!! Thanks for the great story.

  22. Niblick

    I never… in my long, long life…EVER heard of anyone swallowing their cherry pits.

    Who’d a thunk??? (Certainly not the magnificent macerator manufacturer!!) LOL

  23. Carson

    This was too cute so glad it wasn’t more serious….

  24. Jack Lev

    WOW… fixing your Macerator can really be “the pits”!!
    That story is really “Pit-i-ful!!”
    Perhaps she should have made a “pit stop” in another bathroom!

  25. Carl C

    This is a very informative read. I’ve been a full timer for ~2 months now and I’m still learning. Fortunately, my MH doesn’t have a macerator; however, I never gave this ‘Cherry Pit Problem (CPP) any thought before. Dis-solvable TP, yes. “Solid solids” no. Thanks for keeping me on my toes and out of the repair shop!