The Best RV Black Water Tank

In this article we go through everything you should know about the RV black water tank (sometimes mistaken as an RV septic tank), including common issues, how to keep it in top condition. 

How to Find the Right Black Water Tank Size

Question: What size septic tank does a 1995 hornet travel trailer have? It’s 28 feet long.

Answer We really have no idea, but can offer some suggestions. Start by contacting the current manufacturer – Keystone. It seems that your travel trailer was manufactured by Damon which was taken over by Keystone. Here is a link to : contact Keystone.

Here are some other suggestions:

1 – Find the owners manual or look for a list of features for your RV. Our motorhome has a sticker in a bathroom cabinet that tells me how large my holding tanks are.
2 – Locate the holding tank and try to see if it has any marking that tell you how many gallons it holds. This may require crawling under the rig to find the information.
3 – If all else fails start with an empty tank and try filling the tank one gallon at a time, keeping track of how many gallons were used to fill the tank. It is slow, but accurate unless you have solids that have built up in the tank over the years. If there are solids built up, then you may need to have the tank professionally cleaned. Then you can try filling the tank one gallon at a time.

Preparing Your Black Water Tank 

Question: We have purchased a new 5th wheel and previously I read an article that told you how to prepare your black tank with a slicking agent – “Calgon” and hot water – to help the tank remove waste. Do you know the procedure for this application?

Answer: We have never tried it ourselves, but we did find a link to the “Geo Method” procedure you reference. We can’t offer an opinion on this, but here is an excerpt and the link to the full post:

RVs are equipped with waste water HOLDING tanks; NOT septic tanks. The RV septic tank is a misnomer. Those holding tanks are nothing more than chamber pots which should be cleaned and sanitized after their contents are disposed of. The Geo Method is based on this fact.

    When camping and connected to a sewer/septic intake, leave the drain valves closed until the tank is full and ready to dump. This provides sufficient water to flush solids from the tank. Leaving the drain valves open allows the water to drain off without flushing out solid waste. That solid waste will collect in the tank(s) and cause problems over time. If your tanks are not full when you are ready to dump them, fill them with fresh water first, and then dump them.
    This means first dump the black (toilet) water tank first, then gray water tanks. This way you will be flushing out the sewer hose with progressively cleaner water.
    Buy a couple of boxes of powdered water softener – Calgon Water Softener preferred because it dissolves quickly in water. Dissolve two (2) cups of the water softener in a gallon of hot water. Then, pour the solution down the drain into the empty tank. Use two cups of softener for each wastewater tank in your RV. The tank’s drain valve should be closed. Add a cup of laundry detergent at the same time as you add the water softener. Then use the tank normally until it is full and drain it normally. With softened water, wastes washes away instead of sticking.

Read the complete instructions here.

Feedback on the Geo Method:

Reader 1 – After our first time dry camping and dumping our tanks our trailer had an awful smell a couple days later. We found the geo method online and decided to try it since the so called tablets were not working. We have since dumped our tanks 3 times after using the geo method each time and still have yet to smell any odors in our trailer!

Reader 2 – I’ve tried the GEO method. I think there’s something to it! 🙂

RV Black Water Tank Antifreeze

Question: Should I put plumbing antifreeze in the septic tank (black water/toilet) along with the septic treatment? I’m going snow skiing for 3 days.

Answer: It really depends on the temperature where your RV will be parked. If it is going to stay above 32 degrees, and assuming you have the heat running inside the rig, then you should be okay without doing much of anything. 

If you are going to be in below-freezing temperatures for most of the time, then you can add good quality non-toxic RV antifreeze (one designed for RV use) to the septic system. You may not need to add a septic treatment to your black water tank if you are only going to be gone for three days and plan to flush the tanks soon after your get back from your skiing trip.

However if I were you, I would determine if the RV has insulated/heated tanks. If the tanks are insulated/heated and you keep the inside temperature of the RV at 55 degrees or above you should not have a freezing problem and you will not have to do anything different for your trip.

If the tanks are not insulated/heated and you are going to be in very cold temperatures, then you face a much bigger challenge. Your RV may not be designed to handle winter weather. If the RV is not insulated for winter use, you run the risk of burst pipes, cracked tanks and water damage.

Again, what you do to prepare is weather dependent. Note that if it is below freezing, you might find that your fresh water source at a campground freezes. If you expect your three days to have extremely cold weather you should completely empty your all your tanks, especially the fresh water tank, to prevent things from freezing and cracking. Keep the interior of your RV at 55 degrees or higher to help heat your tanks. For drinking, cooking, washing, and flushing, use bottled water. Every time you pour water down a drain, you will also have to pour some RV antifreeze down the drain to keep the plumbing and tank from freezing. Use a mixture of bottled water and antifreeze for flushing the toilet. Just make sure not to dilute the antifreeze mixture too much or it will freeze.

We have spent three winters in very cold weather in New York/New Jersey, but we have a well-insulated RV. We were also completely set up for a long-term winter stay with the use of heat tape, insulation, light bulbs in the plumbing bay and under our rig, and so forth.

Obviously for a three day trip, you are not going to go to all this trouble. And if you expect to have moderate temps and sunshine where you are parked, then things should be pretty much business as usual.

Changing Black Water Valve to EZ Valve

My husband is getting older and so it is difficult to get down to pull valves, especially for the black water tank. We bought a EZ Valve electric valve. Where is the best place to get the AC Power to it? This is on a 2005 Keystone 5th Wheel Camper. Our son will install it. Thanks!

Answer: The best advice we can give you is to follow the manufacturers instructions as to where to source the power. By the way, most if not all electric waste valves need 12 volt DC power instead of AC power.

Another thought is that you may want to run the power from your converter if you have a spare fuse available. That way you can extend the power from the converter instead of the battery, unless the manufacturer specifies otherwise.

Smells from Your Black Water Tank

Question: We have a 2000 Gulf Stream Palm Breeze. When the wind blows a certain way we get a horrible sewer smell in the storage compartments of our coach. It permeates the inside of the coach. We have changed the valves under both sinks and have check the vent on the roof. We seem to only get this smell when the wind blows. Help please.

Answer: A difficult thing to figure out, but we will venture a guess that perhaps there is a break in one of your vent pipes that run from the black or grew water tank up to the roof. If there is a break anywhere along the pipe that could cause the leakage of sewer gasses up into the interior of your RV.

Another possible source are your p-traps, so make sure that you clean them out periodically; use any biodegradable enzyme to break down bacteria and solids . Also, try to keep the p-traps full of water while moving and when stationary. We also recommend that you keep your dump valves closed to further prevent sewer gasses from entering through the dump valves while connected to a sewer connection.

Response 1: We just took off for the first time in our motorhome up to Duncan Mills. When I was unpacking from the back compartment I kept smelling a sewer smell. I did not say anything to my husband because it was slight. 2 days later I was positive
we had a sewer leak. It was getting stronger. I finally broke the news to my husband and we tried to find the source – where it was getting stronger but could not locate where it was coming from. The smell was everywhere. I finally figured out what the smell was when I went to cook dinner. First time trying to light the stove unsuccessfully I realized where it was coming from. Propane smells like rotten eggs. They had overfilled our propane tank.

Response 2: We had that and it turned out to be old water in the washing machine. We ran the washer and the smell left. Now we run the washer every month.