RV Plumbing Systems
Black and Gray Holding Tank Maintenance
It used to be, back when campers camped in tents it was okay to dump gray water on the ground. When campers first moved to travel trailers is was still okay. Then campers wanted toilets in their RVs and holding tanks on travel trailers became necessary. For a while gray water could still be drained onto the ground an only black water had to be disposed of at a dump station.
Of course that’s no longer the case, mostly anyway, but it helps to explains why the sanitation system on most motor homes, travel trailers and fifth wheels consists of the toilet which drains into the RV’s black water tank and the bath tub/shower, wash basin and kitchen sinks which drain into a separate gray water tank. Each tank has it’s own valve but they usually dump through the same sewer connection. There are exceptions to this… sometimes bath water will drain into the black water tank.
Nowadays it is generally not acceptable to dump gray water under any circumstances so a few RVs are being built with one combination gray/black tank. The advantage is mostly to the builder because there is less plumbing to do do. But the combination tanks are necessarily larger and it is hard to find a place for them so most RVs still have two tanks.
RV Gray Water Tank
Since only sink and bath water collects in the RV gray water tank it needs less attention than the RV black water tank.
Most people use so much water whenever the RV is hooked up for a few days, they find it convenient to leave the gray water tank valve open.
If you use the RV for more than a week with the gray water valve open then it’s a good idea to close the valve, add holding tank chemical and allow the tank to fill. This helps flush out any buildup of stuff from the kitchen sink and keeps the tank fresh. It is quite possible for a gray water tank to get very stinky unless it’s flushed periodically.
RV Black Water Tank
The RV black water tank needs more attention primarily to control odor but also to keep solid waste and toilet paper from collecting and plugging the drain line and valve.
The black water drain valve should be left closed until the tank is 2/3rds or more full. This helps avoid the solids building up right under the toilet and assists flushing everything out. If the tank is not 2/3rds full when it is time to break camp, simply add water through toilet.
It’s a good idea to close the gray water valve the night before breaking camp. Then when it’s time to unhook, drain the black water tank first then the gray-water tank thus flushing the black-water completely through and ‘rinsing’ the sewer hose. The procedure works but I don’t always remember to close the valve the night before.
Use a rinse wand which attaches to a utility hose and goes down through the toilet into the black water tank. It really works fast at flushing and rinsing the tank. With all the freshwater going into the tank eventually the sewer hose is flushed clean also.
You don’t have to rinse the black water tank every time you dump but an occasional rinse does help control odor especially during the hot summer months.
Please don’t take the time to flush your holding tanks when there are people behind you waiting for their turn at the dump station. Flush your tank when you are at a campsite with hookups or if you’re sure no one will be needing the dump station.
After the black water tank is drained and flushed close the valve and add enough water to cover the bottom of the tank and then add the tank chemical.
RV holding tanks are just that, holding tanks. They are not mini septic systems. I can’t imagine any serious bacterial or enzyme action happening in the two to four days that most RVers ‘hold’ their black waste. If that were the case we wouldn’t need 3″ sewer hoses or macerator pumps. The only reason for using chemicals in the black tank is for odor control.
What You Should Know About RV Holding Tank Chemical Additives
There are many brands and kinds of holding tank additives all claiming to control odor and dissolve solids. Each one has it’s proponents who will tell you it is the best. For me, all I can tell you is take your pick.
Many RVers recommend enzyme-based chemicals which use live bacteria to breakdown and digest the odor causing waste. I’ve had fair results with some of them but so far I have not found a standout favorite and none of these enzyme based additives does a really good job of controlling odor.
I don’t think there is any difference between the liquid and dry as far as how they work. We like the dry packets because they store better, but they also create dust when poured which we don’t like to breathe. So we generally go with the liquid formaldehyde.
After you have drained and rinsed the black-water tank, close the valve and add enough fresh water to cover the bottom about an inch deep. Then add the chemicals. Add the chemicals a little at a time as you ‘flush’ the toilet. It helps disburse the chemicals.
Waste Water System
The wastewater system inside the recreational vehicle is self-contained, while on the road or set up in a campsite. The main parts of the waste system are the toilet, holding tanks and tank dump valves. As in residential households, the drainage system also includes p-traps and roof vents to allow escape of odors and gases.
RV Waste Holding Tanks
Waste water is divided into two categories: Black water and gray water. The term black water refers to the waste flushed down the toilet and stored in a separate tank*, referred to as the black tank. Gray water is the wastewater from the sinks, tub and shower drains and is stored within one (or more) gray tank(s). Waste tanks empty through a single outlet, but a separate valve controls each tank.
The dump valves should remain closed even if connected to an exterior sewer hook up. For proper dumping, empty tanks only when they are nearly full. The idea is to send a large volume of water through the tanks and hose at the same time to assist the solid waste in flushing from the system.
RV Waste Holding Tank Dumping Instructions
- Place the end of the sewer hose into an approved dump station inlet.
- Twist off the termination outlet cap.
- Connect the sewer hose by turning counterclockwise, locking the end levers over the termination end.
- Open the black tank termination valve and drain.
- Open the gray tank termination valve and drain. (If RV has 2 gray tanks, drain one at a time.)
- 6. Close termination valves.
- Disconnect sewer hose and store.
- Replace termination cap on the outlet.
- Add chemical deodorant / breakdown agent approved for RV use.
After the sewage tank has been emptied, close the gate valves and put approximately five gallons of water in the sewage holding tanks. This will help prevent solids from building up. The addition of a deodorizing agent like Aqua-Kem® will help prevent odors.
The toilet operates from water supplied either by the fresh water tank or from an exterior water supply connected to a campground water hook-up. (The water pump must be turned on when utilizing the water from the fresh water tank.)
The toilet flushes directly into the black water tank. You should find complete instructions and care for the model installed in your RV at the manufactures web site or by calling the company.
The most common problem associated with the waste system is solids build up. Using plenty of water when flushing the toilet, and keeping the holding tank valves closed until ready to flush the system can reduce the risk of build up.
Should you ever have a build up of solids, close the valves, fill the tanks at least 3/4 full with fresh water, drive a drive a few miles to agitate the solids then drain the tanks.
Do not put these items in toilet
- Facial tissues, paper towels, sanitary products (including those labeled flushable).
- Detergents or bleach. Use a sewage tank deodorizer.
- Automotive antifreeze, ammonia, alcohols, or acetones.
- Grease from cooking, table scraps or other solids that may cause clogging.
RV sewer hose
You need an RV sewer hose to connect the RV drain valve to the RV park’s sewer line or dump station. Unless you use your RV only a few days a year it is recommend you get a heavy duty hose. They cost just a little more but they’re worth it.
Most of the time you will need 10 feet of hose or less but if you travel enough you will find a time when you’ll need more.
Carry a 6′, one 10′ and a 20′ hose each set up with valve adaptors and sewer connectors. Also carry two hose connectors. By using the connectors to join hoses in different combinations You can get a length at least close to what you need without have a lot of extra hose.
You can also have a heavy duty hose about 4′ long ( the piece remaining from cutting a 10′ long hose to six feet ) with a hose adaptor on one end and the bayonet fitting on the other. This is a dump station hose. The hose adaptor fits down the sewer pipe and help prevent the hose from pulling out while dumping.
You can use the red EZ threaded plastic couplings made by Valterra to make up the hoses.
Whenever the sewer pipe has a threaded end you can use the sewer thread attachment in addition to the universal sewer connector. This assures a good leak proof connection. Some parks require their use.
You should usually replace at least one of the hoses each year. Sometimes you can buy a 20 footer and make up all new 4′, 6′ and 10′ hoses since these get the most use.