Holding Tanks

Almost all travel trailers, fifth wheels and motor homes have holding tanks for the fresh, gray and black water. Pop-up tent trailers may only have a small fresh water holding tank and no holding tanks for gray or black water.

The fresh water tank is for just that, fresh water.

The “gray” tank holds the water that goes down the drain in the sinks and shower.

The “black” tank holds the waste and water from the toilet. This tank needs to be treated with chemicals to break down the solid waste and to control odors. Pop-up trailers usually use a “cassette” toilet that still needs some chemical treatment to combat odors and break down the waste.


Chemicals

There are special chemicals you should use, especially in the black tank, to reduce odors and the buildup of solids in the tank, which would cause you problems down the road. There are many brands and types on the market, from powder to liquid. Regardless of the type, it is usually recommended (or required by the campground) not to use chemicals that contain formaldehyde, which is a chemical that is harmful to some septic systems. I prefer the liquid type because I can also put a little in the gray tank via one of the sinks to help control some of the odors that can come from there under the right circumstances. Since the chemicals are also designed to help lubricate the dump valves, this is another reason for putting a little in the gray tank.

Most of the black tank chemicals advertise that 4 ounces will treat a 40-gallon tank, but there are times where you could use more or less than 4 ounces for that 40-gallon tank. Some brands require a “double dose” in hot climates (Arizona in the summer). But what if you’re just going camping for the weekend? Are you going to fill up that 40-gallon tank in one weekend? Possible, but doubtful.

Here is what I do at the end of the weekend. When I’m ready to leave, I dump and rinse the black and then the gray tank (more in this later). When done outside, I go back into the trailer and flush the toilet 5 times (using the one lever to fill the bowl, about 1 gallon, and then flush with the other lever). On the last flush, I add just 2 ounces of chemical to the bowl. This is enough water to cover the bottom of the tank and will slosh around on the drive home allowing the chemicals to “attach” themselves to any solids that might be left in the tank and clean them up a bit.

If I am on a trip and staying a day or two here and a day or two there, I’ll wait until the black tank is 2/3’s full before dumping. It is only a little extra weight to be hauling from one campground to the next, but it gives the chemicals a chance to work on what they are supposed to do…break down the solids.

If you park your RV in a warm or hot location while not in use, you may want to add water to both black and gray holding tanks occasionally to keep the dump valves from drying out. Since I already know that my toilet bowl holds about 1 gallon (I used a milk jug to measure it), I use that as the gauge for how much water may have evaporated from the holding tanks. When I park the trailer and don’t know when I’ll be using it again, I’ll fill up the toilet bowl about half way and check it occasionally. When it is almost empty, I will fill and flush the toilet two or three times, figuring that there is more surface area of water in the holding tanks, which makes it easier for the water to evaporate faster. Same thing for the gray tank. The bathroom sink holds about half a gallon and each side of the double sink in the kitchen holds about 4.5 gallons. I fill the bathroom sink all the way and the 2 sinks in the kitchen about half way. When half of the water has evaporated, I pull the drain plug on all the sinks and refill. This helps prevent odors from backing up through the pipes because by this time, the P-traps have also dried up. Keeping water in the sinks and toilet also act as an odor barrier. And don’t forget the shower drain. It may not be possible to keep water in the bottom of the shower, but plug the drain when not in use and pour water down the drain at the same time you are draining the sinks.

Before leaving for a trip, check the toilet for any odors coming from the black tank. If you smell any unpleasant odors, go ahead and add maybe an ounce of chemical and a few gallons of water to slosh around on your way. Check again on your arrival at your destination. If you still have odors, you could either repeat adding a little chemical and water or dump and retreat the tank. And if you have filled the toilet bowl and sinks to use as an evaporation monitor, don’t forget to drain them before you leave on your trip. You don’t want the water sloshing around.


Dumping the tanks

When you arrive at your destination, you can go ahead and hook up the sewer hose to the RV and to the dump hookup if you like (or you can wait and do it when you need to dump), but leave the dump valves closed until you need to dump the tanks. This will do a couple things. First, it will prevent odors from the campground sewer system from backing up into your RV. Second, it will give the chemicals in the tanks a chance to do their job.

Watch the monitor panel inside the RV for when your tanks are getting full. If it is getting close to your departure date and the gray tank is getting full, go ahead and dump some of it if you need to, but don’t empty it completely. You’ll want some of the gray water to use as a rinse of the sewer hose after you dump the black tank. You can let both tanks get completely full before you need to dump them, but you don’t have to if you don’t want to. Just make sure you leave some in the gray tank to rinse the sewer hose after dumping the black tank.

The recommended sequence of dumping the tanks is, first the black, then the gray. The water from the gray tank will act as a rinse of the sewer hose. Many RV’ers also recommend rinsing the tanks after dumping, and there are several products on the market to do that with. Here are links to just a few:

Sewer Solution

Flush King

Quickie Flush w/Accessory Kit (sorry, no direct link, but available from most RV supply stores). Sometimes you'll see both pieces sold as a No Fuss Flush.

The first two are devices that attach to the tank dump pipe and backfill water into the tanks. The Quickie Flush is something that is partially inserted into the tank that has a multi-directional spray nozzle that is inside the tank with the connecting hose on the outside of the tank. Although the Quickie Flush requires some installation work (which is relatively simple), it uses less water than the other products.

There are also a variety of “wands” that can be inserted through the toilet into the black tank which reportedly also do a good job of rinsing the tank, but this would involve attaching them to a hose and getting the hose and wand into the RV. Personally, I prefer to do this job completely from outside the trailer.

When dumping the tanks, it would be a good idea to wear some rubber or disposable gloves to protect your hands when handling the sewer hose and connections. When finished dumping, use the water faucet or hose outside to rinse the gloves off or throw the disposable ones away. Place the gloves and any connections that do not fit in where the sewer hose is stored in a separate and sealed storage container away from any other hoses or accessories you use.


Where to dump?

That may sound like a silly question, but what if your campsite doesn’t have sewer hook-ups? If that is the case, usually the campground will have a “dump station” that you can use. The dump station is usually centrally located within the campground, perhaps as you exit. You may need to share it with your fellow RV’ers, so be patient.

What if the campground doesn’t have a dump station or there is something wrong with it? Then you will need to find another approved dump site. Try searching www.rvdumps.com for a place along your route. Some sewage treatment plants may have a hookup you can use, but you will need to seek them out.

Can’t I just dump them on the ground? Absolutely not!!! Obviously the black tank is going to smell and would be an unsightly mess for others to endure. And even though you might think the gray tank may only contain soapy dishwater or shower water, it could contain harmful bacteria or human fecal mater that would be harmful or deadly to plants or animals.

Not only would it smell and make a mess, many cities and/or states have laws against such dumping. Here is a link to a site all about gray water and here is a link to its page about state laws.

What do you do if you don’t have a sewer hook-up at your site and you plan to stay for a while and need to empty your holding tanks? Simple! Get one of these portable “tote tanks”. You just dump the contents of your holding tank into one of these and “tote” it off to the dump station. Although most people would recommend using a tote tank for the gray water, you could use it for the black water if you need to. Just make sure to clean it out really good. Use 1 ounce of bleach for each gallon of capacity to sanitize, and rinse out thoroughly. Use the campground restroom facilities as much as possible to avoid this situation, if possible.


Sewer hoses and connections


Toilet Paper

What type of toilet paper should you use in your RV? Almost any 1-ply and some 2-ply toilet paper should be just fine, but there is a simple test you can do to see if your brand will work okay in the RV. Take an empty mayonnaise or pickle jar (or something of similar size) and fill half-way with water. Put 2 sheets of the toilet paper in and put the lid on. Shake for about 10 seconds. Has the toilet paper begun to break apart? If so, it should work fine in your RV holding tank and the chemicals you use should be able to break it down. Some people report being able to use 2-ply without any problems while others have reported some problems using 2-ply and having problems with the tank level sensors. I’d suggest just getting the 1-ply and use twice as much if you’re used to using 2-ply at home. It might cost a little more to do it that way, but it beats the cost of replacing the black tank or dealing with faulty sensors.


Flushing

Now here is a touchy subject, so I’ll try and explain without getting technical.

The process in our trailer is simple (sort of)…any time anything solid is going down the toilet (like the toilet paper), you fill the bowl with water and then flush. If you are using the toilet to dispose of your own personal “solid waste”, hold the flush lever down while dealing with the task. This allows the solids to go directly into the holding tank as the water does a little rinse job on the bowl. When “the task” is complete (or almost), you can release the flush lever. Finish up with the toilet paper, fill the bowl with water and flush.

Okay, I hope I didn’t embarrass anybody, but this helps to ensure that there is enough water in the holding tank for the chemicals to do their job…break down the solids. So far, I have not had any problems with the holding tanks or with solids building up inside them.