Control Tank Odors With This Simple Trick

July 19, 2011

One secret to controlling odors and extending the life of your RV holding tanks is to add plenty of water to the black water holding tank after you empty it.

How much water should be added?

You want the bottom of the tank to be completely covered by water and depending on the size of the tank this might require 3 toilet bowls of water or it might take 7 or 8 to completely cover the bottom of the tank.

What else should we keep in mind?

Add plenty of water to the bowl every time you flush it so there is enough water in the tank at all times to assist in controlling odors.

Happy RV Learning!
Mark Polk


  • Pete Montague

    In addition to keeping water (cover the bottom) in the black water tank you should also add whatever you are using for odor control. I also add some Dawn liquid detergent or sometimes something like Lysol so that as you drive, the sloshing motion in the tank helps to clean the sides and the sensors for the tank monitor system. It also helps to keep the smell down while the vehicle is parked between camping trips.

    Question for Mark Polk. Since most of us use a lot more gray water than black yet the tanks are usually the same size, why aren’t the gray water and black water tanks connected so as to allow more storage of gray water when one has to move the unit to a dump station (i.e. no sewer drop) such as in most state parks, etc.?

    • Tom Woodman

      Joining tanks may cause odors and bacteria to invade shower and sink drains. Even though the drains have p-traps, the sloshing of full tanks during rough travel may move bad stuff up the drains and into the trap water. There are rare times when traps run dry, leaving no barrier to the odor.

      Do not mix tanks!!

  • Lance

    While a plumber in the Air Force and an Industrial Maintenance Mechcanic after leaving the service, I have done the following a few times on metal tanks and it worked. Depending on the location of your black and gray tanks to each other, and the clearance below the floor you can try this: Come out of the top of your gray tank with a long sweep 90 degree elbow, run a flexable line (hose) over to the black tank, and place a long sweep 90 degree elbow in the top of it. Place a check valve in the line, close to the gray tank to prevent backflow. Since it is a drain line it should be lower at the black tank to allow for drainage. I would recommend a 1″ line, but the size is up to you based on your usage. Before starting this you need to conceder if the thickness of you tank will allow this re-work. Most plastic tanks need a mounting block added. Hope this helps.

  • Tom

    In an RV it is much better to have the gray & black tanks separate. If they were connected, what do you think would happen if the tank/s filled-up? I sure wouldn’t want black water backing up into the shower or sinks. Besides this…it is really nice to have a pretty full gray tank/s that you can dump after the black tank has been emptied. The soapy water from the gray sure flushes out the sewer hose.

  • Larry Brabec

    A little off subject, but try a bag of ice in your black water tank when moving on. Works wonders for cleaning your tank and level indicators.

  • Rod

    We’re experienced (42 years) campers and have tried many different ideas
    for keeping holding tank odor under control. First and foremost, be sure to “water” your traps after the RV as been sitting idle for some time. I also mix one cup of Pine-Sol in a gallon of water in both the gray and black water tanks as soon as I have emptied them. This gives you great cleaning action on the road, and provides a pleasant scent. No substitutes, though. Spend the money and use real Pine-Sol, still much cheaper than the chemical treatments that are on the market.

  • Doug Howland

    I have a question for Mark as well – why is it that all RV manufacturers make both the black and grey water tanks the same size? I have yet to meet another RV’er who has ever filled their black water tank before the grey water tank. A 2:1 ratio would work much better in my mind… anyone know why?

  • Suzanne

    Should we be putting water in the grey tank after it is empty too? I have been putting a splash of vinegar in it. Is that bad?

  • Bill Tinsley

    I am a commercial motor coach operator that can help with tank odors. In the coaches, the top tank is open to the inside air so odor becomes more of a problem than with a closed unit. Add Snuggle Fabric Softener, Exhilirations brand. The scent is pleasant and it has enough soap in it to clean out the sides of the tank during transit.

  • Lyn

    there is a small hole in our air mattress of the couch fold out bed. the patch kit that came with the trailor, dried up, it was never opened. we went to the camping supply stores and they dont carry the repair kits. we were told to go toa boat supply store. we are concerned that the glue may desolve the mattress (plastic) if not carefull and there isn”t a name on the tube.

    • Jim

      I have used contact cement is used in patching my air mattress, this is the same stuff used in bycyle tube patching kits…. should work for you

  • Kate

    In regards to holding tanks registering proper readings, I was wondering if TSP in the tanks would help clear the gunk. Is it safe for the plastic holding tanks?

  • Julie

    I read somewhere about putting Calgon water softener in the black tank, filling it and then driving. the movement cleans the sensors- ours are forever reading full. is there anything that i should never put in the black tank- cleaner wise- as it might cause damage to the seals or whatever is in there? i was thinking of putting some simple green in instead of pinesol as someone suggested.

  • Tom Boyte

    After we drain our tanks, both black and gray, we add two cap fulls of Calgon water softner to about 5 gals of water in each tank. The Calgon makes the tanks interior slick and everything drains nicely.

  • Ron Story

    After i empty my black water tank some times like onece a month i put a couple bags of ice and pure lemon juice(REAL LEMON).I get the biggest bottles i can find and the cheapest.Dump it in and drive down the road..Just leave it in til you dump again. Cleans and smells good..

  • Ken Cresdee

    Regarding the thread on tank odors, I am concerned with the issue of using any products that would be harmful on the seals and also on using products that biodegradable. Therefore if you used something like Dawn or Pine-sol should you also use another product help break them down. Most parks are very concerned about what goes into their drains today. Lastly, I think this can be more of a problem if you use your unit for longer than weekend use. We full-time and are beginning to wonder if leaving the grey tank open is wise. Perhaps we should also be closing it and emptying it every few days. Any comments from other full-timers would be welcome.

    • Gary Hill

      We spent two years full-timing in ONE spot – – didn’t move as we were building a house. Leave the tanks closed until 2/3 full then dump. I put RID-X in the tanks, not those expensive RV chemicals. I never had a problem, no smells, and the septic tank that I dumped into loved it.

    • Hope


      As a Campground owner (& camper), over the years I have noticed many problems with leaving Gray, as well as Black, tanks open. When you are washing your dishes food particles inevitably will go down your sink drain. These food particles will also stick to the sides of your Gray tank and may end up ‘caking’ and causing future problems. It is always best to let tanks fill at least 3/4 before dumping…this ‘rule of thumb’ is in the manual for a reason and not just there to ‘frustrate’ the camper. Keeping your tanks healthy and clean is the best way to avoid odors! Don’t leave valves open, don’t use non-RV chemicles in them (seals may be effected by harsh chemicals), and make use of de-odorizers like Gray water odor control for gray tanks, and RV recommended Toilet chemicals. AND ALWAYS USE RV MARINE OR 1 PLY TP!!

  • Cheryl Stroup

    If I was to add some Dawn of Pine Sol to my black and grey tanks, is it still safe to add the regular critters? I love the idea of cleaning the sensors but we like to have critters in the black tank. Thank you.

  • Brian Wood

    I always add a couple spoonfulls of baking soda and then follow it with some vinegar in all my drains. It is a cheap and non chemical deodorizer, it’s safe for the tanks and no odors after.

  • Paul N.

    As far as putting chemicals in the holding tanks, Do not use any product that say’s contains petroleum anything. Tanks and there plumbing systems are made out of polybutulene and ABS. These chemicals over time will destroy these types of plastic.
    Take into concideration that the sensors and the metel parts of the valves are stainless steel if using acidic products just rinse with fresh water. Keep traps in sinks and tubs full of water while stored. there are vents on the roof that allow the sewer gases to escape the tanks, just like your house. Don’t park unit to close to second floor windows. Leaving some water in the tanks with the chemicals made for holding tanks while traveling and waiting to go again,will help to eat the waste particals stuck to the sides and help with oder. Just remember there holding tanks there going to smell no matter what you do.

  • Elizabeth Willson

    Hi there: I often pour my dish water down the RV toilet so that our gray water tank does not fill up so quickly. We move around alot in our 18′ Sunline Travel Trailer so we use the dump out stations at the campgrounds. Max stay is usually only 3 nights and we can do this if I pour the disp water down the toilet and use the campground showers.
    #1 – will the dish detergent harm the black water tank or interfer with the decomposition?
    #2 – I just recently poured a butter knife down the toilet! I know stupid! But I did do that when empting the dish water. Any hints on how to get it out?
    So far it has not interferred with the dump outs.

    Thanks for your words of wisdom.

    • Peggy Bates

      We traveled around US and Canada for a year doing the same thing! I think that’s why we never encountered smells in the rv. We never added any of those high priced rv chemicals, never seemed to have the need. We stayed in campgrounds like you, about 3 days max. We would dump before leaving, add some water to the black tank and maybe a little Lysol, that made everything seem fresh! I don’t think the dish water would harm the seal/tanks because it’s probably the same construction as the grey tank? The excess of water, I think, was beneficial during our time on the road. The rv has been sitting now for 2 years, with occasional use, and has no odor at all!

      • Elizabeth Willson

        Thanks, Peggy: Your comment was encouraging. We live near Ottawa Canada and will not be travelling to Orlando to have our tanks cleaned.
        Our interests are fly fishing and hiking.


    • Peggy Bates

      We aslo did a monthly clean out with a wand, sold at Camping World. We also put 2 spoons down the toilet, they eventually came out! Just keep in mind that they are there, because we were reminded both times when we couldn’t shut the clean out (spoon stuck in between!) had to reach up and get it out. Good to hear someone else did that!

    • Marie in VA

      Hi Betty, sounds as if you need to travel to Orlando — read the next two emails and you will see what I mean. Good luck

      • Elizabeth Willson

        Hi Marie: We live near Ottawa, Ontario, Canada and will not be travelling to Orlando with our small travel trailer. Our travel interests are fly fishing for trout and hiking.

    • Corky

      For the butter knife in the tank. Have you tried a magnet on a string down the toilet?

  • Tami N Gammill

    This dialog is very helpful! Thank you all so much!!

  • Donna Rock

    When all else fails then had to Orlando, Fl. There is a company, All Pro Water Flow, 321-446-0175, who will professionally clean out your black, gray and water heater tanks. They come into the park and use some type of power sprayer to bust up your solids, clean your sides and sensors. We just make it a routine visit to Orlando and have the tanks cleaned. It is not expensive and your worries are over for the next couple years The guy can show you the interior of your tank and it look brand new. Our coach is nine years old and we are full timers so our tanks are used daily. Give this company a call we do.

  • Marie in VA

    Really enjoyed reading everyone’s ideas and all of this is well and good if you are traveling often. When our RV sits for a period of 1, 2, or 3 months, the hot water smells so bad that you cannot stay inside. I am sure that some type of mold is in the unit. I know that you are not suppose to use Clorox products, but if we pour about 1/4 cup into the water hose, then connect the hose to our household outside spiget and flush the lines it will not smell again until it sits for at least a month, then we have to start all over again. We just cannot figure out what we are doing wrong, but we sure are doing it. I keep thinking that when we winterize it, the problem should go away, but it doesn’t. Please help with this stinky and probably unsafe problem!!

    • Bill Mullins

      To keep the smell out of your water heater all you need to do is drain it when you get home and before you store your unit.
      The water heaters without the anode rod seem to have this problem worse than the ones with. You’ll need to buy a deep 6 point socket to fit the drain plug of the heater and some thread paste, but all in all its a simple and effective way to avoid the rotten egg smell in your hot water