Yesterday, I dumped and flushed our holding tanks. I’ve written that sentence in this blog many times. It’s not the most pleasant task or subject, but I’m going to write what I know about it today.

To be self-contained, an RV must have the ability to store and pump fresh water. It also must be able to store wastewater for proper disposal. Fresh water capacity is usually the limiting factor regarding how long you can live without hook-ups. In some cases, gray water capacity may set the limit.

Most self-contained RVs have three water tanks – fresh water tank, gray water tank and black water tank.

Fresh water is potable water stored on board and is usually pumped through the plumbing with an electric pump. I always filter the water going into our motorhome. I never know if the water supply I’m hooked up to had recent work which may have left sediment or dislodged rust into the system. Our current set-up is a two-stage canister filtration system. The first stage is an inexpensive 5-micron spun-polypropylene filter that traps sediment or other solids. The second stage contains a 5-micron fiber-block activated-carbon filter. This filter removes chemicals, bacteria, lead and other heavy metals. We have another filter on a tap in the kitchen that is a one-micron carbon filter that will remove giardia and cryptosporidium cysts.

I always use a pressure regulator on the fresh water supply. I wrote about that here. Our fresh water supply comes directly from the RV park water supply when we’re hooked up. When we don’t have a fresh water supply hooked up, we draw fresh water from our 100-gallon fresh water tank (total capacity is 110 gallons when you add the hot water heater volume).

So where does our fresh water go when we use it? The shower drain, kitchen sink and bathroom sink drain into the gray water tank (on some RVs, the bathroom sink may drain into the black water tank). Clothes washing machines and dishwashers also drain into the gray water tank. Gray water is generally considered to be harmless to the environment. Every drain has a P-trap. This is a U-shaped bend in the plumbing to trap and hold a small amount of water. This prevents the flow of gases from the tank coming out of the drain. Gray water can smell bad due to organic matter breaking down in the tank.

The tank has a vent that is piped up to the roof of the RV. It also has a drain pipe with a blade valve that exits under the RV. When we’re on full hook-ups, we aren’t concerned with how much gray water we create. We take regular showers and run the washing machine. I drain the gray water tank after two or three days – we have 100 gallons of gray water capacity in our coach. We average about 30 gallons of gray water per day for the two of us plus maybe another 8 gallons of black water. When we dry camp, we practice water conservation and use about 15 gallons of water per day. According to the Environmental Protection Agency (EPA), the average household uses a total of 80-100 gallons per person per day.

The toilet flushes into the black water tank. It’s important to understand how the black water tank functions. The most important thing is to have plenty of water in the black water tank. Solid waste matter and toilet paper needs to break down in the tank. If there isn’t sufficient water in the tank, solid waste can accumulate in one spot (below the toilet) and create the dreaded poo-pyramid.

Most RVers also add a chemical additive to the black water tank. There are many different additives on the market. They all have one thing in common – they claim to eliminate odor. Some mask odor by using scents. Some claim to break down solids as well as paper. Some claim to clean holding tank level sensors. Some of them claim to lubricate the blade valves.

I’ve tried several different brands. My comments on these brands are unscientific. I didn’t test or analyze. I’m just stating my observations.

The Oxy-Kem® brand controlled odors well. But I noticed paper in the black water when I drained the tank using Oxy-Kem®. By the way, it’s important to have a clear section in the sewer hook-up. It’s not a pleasant thing, but you need to be aware of the condition of your tanks by observing the discharge.

I was skeptical about brands that claimed to break down paper. I tried the Odorlos® treatment which claims to liquify all waste and tissue. To my surprise, I no longer saw any paper when I used this product. The odor control was not so good though.

The Walex Bio-Pak®was up next. it says it’s a natural enzyme deodorizer and waste digester. This product also broke down the paper, but isn’t the best odor controller. The packaging also doesn’t say it’s formaldehyde-free. Some holding tank treatments contain formaldehyde which isn’t environmentally friendly.

I’m currently using Happy Campers® treatment. So far, it seems to be the best. It breaks down the paper and seems to control odor well.

I drain the black water tank after five to seven days. Internet wisdom on various RV forums advises to have the black water tank at least 3/4 full before draining to ensure a forceful flow that will get everything out. This rule of thumb doesn’t make sense to me.

My old coach had a black water capacity of 40 gallons. At 3/4 full, it held 30 gallons of black water. It drained forcefully and I had no issues. My current coach has a black water capacity of about 90 gallons. The 3/4 rule means I should have more than 65 gallons before I drain the tank. Why? If thirty gallons worked on the smaller tank, why wouldn’t thirty gallons work on a large tank? They have the same size outlet and drain at the same rate.

I time how long it takes to drain the tank and I have a rough idea of how full the tank is. I usually have about 40 gallons when I drain the black water. We once went for 15 days without dumping tanks and I think the black tank was nearly full then.

Our coach is equipped with a black water tank flushing system. This consists of a hose connector and plumbing to a spray jet inside the black tank. I connect a water hose to the flush system and turn on the water before I open the black water blade valve. Do not use your fresh water supply hose on the black tank flushing system. I’ve seen people do this. Although the system has check valves, back flow is always a possibility. I let the flusher run for 10-15 seconds to agitate the wastewater, then I pull the valve open. Whoosh. After the tank drains, I leave the flushing system running for several minutes, then I close the valve. With the valve closed, I continue to run the flusher for 30-40 seconds to put a few gallons of water in the tank. Plenty of water in the black tank is a good thing. Then I go into the coach and flush the treatment down the toilet and into the tank.

I should mention the importance of having the sewer hose securely fastened to the sewer drain. If it can’t be screwed into the drain, it must be weighted down. The tank drains with enough force to lift the end of the sewer hose straight up and spew the contents. If you’ve seen the movie RV starring Robin Williams, you know what I’m talking about.

Once I’ve finished draining and flushing the black tank, I drain the gray water tank. Running 50 or 60 gallons of gray water through the sewer hose cleans out anything left behind after flushing the black tank. That’s how I do it.

I’m not sure if the cloud cover will burn off today. We have cloudy skies and a 90% chance of much-needed rain tonight.