Recreational Vechicle

HepvO Waterless P-Trap, How big is it?

Frequently folks call and ask us how big the HepvO waterless P-trap is.

 HepvO complete kit

  The HepvO can be installed both vertically or horizontally.


If you are not familiar, The HepVo Waterless Valve replaces the old P Trap with a short tube and internal diaphragm that prevents backflow of air and water into showers and sinks.

The water inlet pipe side of the HepvO uses industry standard thin wall pipe. The output side of the HepvO adapts to both thin wall or sch. 40 or 80 drain waste 1.5″ ABS/PVC piping.

The HepvO® is certified to meet the requirements of ASME/ANSI A112.18.8 and can be installed in new homes and industrial buildings by having the building inspector use the “Alternate Materials section” of the Building Code. HepvO® can also be used to fix existing plumbing systems by replacing p-traps which are suffering from odor or noise.

While the HepvO® is relatively new to the North American market  it is not a new product. It has been in high volume production in the UK since 1997 and it is widely used in Europe, Australia and the Far East. It has attained numerous international approvals against very demanding standards and has achieved an enviable track record of trouble-free performance. There are over 2 million installations worldwide.

How Does that LED light in the switch work on the Drain Master?

How does that red LED light on my Drain Master switch work?  We are asked this by customers about 5 times a week. So we thought it might be a good idea to explain how in detail here.

In simple terms if the light is on, the valve is open (to some degree.)  If it is off, the valve is fully closed.  So in other words, if you close your valve and the light stays on, chances are, something is stuck in the gate path.

Light ON = valve OPEN

Light OFF = valve CLOSED

Now if you are the type of RVer that prefers to know “how” it works, then keep reading for a technical explanation.

Your switch should look like one of these. 



The Magnetic Switch we will be referring to in this article is on the back of the valve and looks like this.






First we need to start with the 12vdc power going to the operator switch from the coach battery. If we use a wire placed on the + (positive) terminal of the battery and run it to a magnetic switch placed on the back of the Drain Master valve and then run the wire from the magnetic switch through an LED light and terminate the wire by connecting it to the – (negative) terminal of that same battery, the LED light would light up.

Now if I take a magnet and place it over the switch on the valve the light will go out, remove it and the light will go back on. What we have done is glued a magnet on the gate in a precise position so when the gate is in its closed position the magnet is lined up under the switch.

Battery + —————-Magnetic switch N/C———-LED light————Battery –

The dash lines indicate the wire.

There you have it, simple and effective. If the light is OFF the valve is CLOSED. If the valve gate is in any other position the light is ON.

If your magnetic switch is not working you can replace it. The part# is 5016 and they are $5.98 ea and come with complete replacement instructions. You can find it here.

Chemical or Biological Holding Tank Treatments, The REAL Facts!

As the typical RV’er stands in the “Toilet Chemical” or “Sanitation” aisle in just about any RV supply store they often become overwhelmed by the number of different holding tank treatments sitting on the shelf. There are blues ones, green ones, orange ones, yellow ones. Liquids, tablets, powders and pouches. Big bottles, small bottles, boxes, bags, tubs, jugs, tubes and blister packs. As you take a step closer and start reading the large print, the confusion deepens. They all claim to do basically the same thing!

So, how is one ever expected to make an informed choice?

The simple answer is, “It isn’t easy.” Knowing that answer isn’t going to be of much help, let’s see if we can somehow demystify the buying decision with some basic knowledge of holding tank treatments.

For the sake of simplicity, RV holding tank treatments generally fall into one of two broad categories: Chemical Treatments and Biological Treatments.

aqua-kem chemical holding tank treatments

A Typical Chemical Treatment

Chemical treatments contain one or more active ingredients that are intended to eliminate odors by essentially halting the waste breakdown process until the contents of the holding tank are emptied to a larger holding facility or a municipal sewer system. The majority of these active ingredients are bacteriostats (suppresses bacterial growth), bactericides (kills bacteria), or masking agents (chemically “locks” odors or attempts to cover them up).

Unfortunately, it has been found that most of these chemicals are toxic to a certain degree and some pose a very real risk to human health and/or the environment. In fact, a number of these chemicals have been under legislative scrutiny for many years due to their potentially harmful effects. The six most commonly used chemicals are: formaldehyde, bronopol, dowicil, glutaraldehyde, paraformaldehyde, and para-dichlorobenzene. All of them have been the subject of various regulations restricting their use in other industries and it is probably just a matter of time before they become regulated in the RV industry.

pure power blue biological holding tank treatments

A Biological Treatment 

pure power green biological holding tank treatments

Pure Power comes in Blue or Green

Biological treatments are based on the principal that adding large quantities of beneficial bacteria to a holding tank will “jump start” the waste breakdown process and control odors by excluding the formation of odor-causing “bad” bacteria. A pure biological formula contains no chemicals and is non-toxic to both humans and the environment. As advances are made in the field of microbiology these types of products, such as Pure Power, now have the potential to outperform chemical treatments in every way. It should be noted that enzyme treatments have also been included within this category because they are biological in origin, but they lack the full performance characteristics of a true bacteria based formula.

Summed up in the simplest manner possible, chemical treatments preserve waste and biological treatments break down waste. Both types are meant to control odor, one does it through chemical suppression while the other does it through a natural biological process. Generally speaking, it takes less of a biological product to control odors than is does a chemical product As the rest of the world goes green, so follows the RV industry.

Cleaning The Sewer Hose After Dumping

The other morning while talking to a customer about his neighbor’s gray tank being caked with Black waste, he mentioned the need to clean his sewer hose after dumping, with fresh water from the spigot.

Lots of folks do this, and quite frankly it is not a good practice, especially if they use their fresh water hose! I have seen people use the fresh water spigot, without a hose on it and put the coach end of the sewer hose up to the spigot then turn it on, yuk!

The proper method to clean your sewer hose before storing, is to leave it connected to the RV and the sewer inlet.

rv sewer hose - gray tank

First dump the Black water, and the Gray water second.

(Most people do this and know it is the right procedure. What they do then, is disconnect the hose from the coach and wash it inside as described above.)

Next close the Gray valve and use the tank flusher mounted in the Gray tank, to fill the tank 2/3rds full.

garnet tank monitor

Then open the valve and let the water go.

drain master valve

If the coach does not have a tank flusher in the Gray tank. (and most do not)
Fill the Gray tank by turning on the taps for the sinks and watch the tank monitor until the tank is 2/3rds full.

drawing of turning on water

Shut off the taps, open the valve and let the water clean the inside of the hose.

If you follow our “First in Last Out” procedure found here you will disconnect the hose from the RV, attach the plug and walk the hose out to the sewer inlet. The remaining water in the hose will drain out of the hose and into the sewer. Remove the sewer fitting. Immediately put the cap on it while over the sewer inlet, or in our case, close the nozzle and remove it.  Then take the hose assembly back to the coach for storage.

RV Holding Tank Flushers What Are they, How do they work?

Flushing RV holding tanks on a regular basis is an important element in eliminating tank blockages and foul odors in and around your RV.

Many types of tank flushers have been produced over the years. The wand was popular for a long time. Folks did not like having to run a garden hose in a window or drag it through the entry door to the bathroom.

wand style holding tank flusher

Wand Style Flusher

While almost all RV Manufacturers put an internal sprayer in the Black holding tank, only a few provide one for the Gray Tank/Tanks.

By far the most popular tank flusher is the No Fuss Flush.

no fuss flush - holding tank flusher

No Fuss Flush

The No Fuss Flush requires a check valve when installed by the RV mfg. and adds cost to the RV which is a big part of the reason it does not come standard on the Gray tank. The device also needs to be installed above the flood plain or above the bathroom sink. They would also need to supply a 3 way valve so the supply hose can be switched from one tank to the other. This is not the case in the aftermarket. An aftermarket kit comes complete with the tank flusher and a water hose inlet port with a check valve in it, making the installation far easier.

A unit called a back flush appeared on the market about 10 to 15 years ago and its purpose was to connect it to the sewer hose connection and run water back into the holding tank.

Back-flush Device

While this is against RVIA code regulations, it is not against the rules in the consumer market. The only effective use of this device we found over time and testing is to clear a blockage in the Black tank without making a mess! With the sewer hose connected to the outlet and to the sewer ground inlet back-filling with the pressure from the water spigot works very well to dislodge tank blockages. As for cleaning out the tank itself, not so effective! Any action created from the spigot pressure is diminished greatly by the turns in the fittings getting to the holding tank. The agitation created by the spray in the internal method is much more effective than back-filling. If you tend to use too much RV toilet paper and not enough water, a back-filling device should be in your waste fitting container–if not, you have spent money and gotten little value.

If you have questions regarding this article or questions in general about RV waste management, we encourage you to contact us via email or by calling our toll free number (877) 787-8833.

Sewer Smell Inside Your RV? HepvO Waterless P-trap to the Rescue

If you have ever had a foul smell in your RV and couldn’t figure out where it was coming from, we may have the answer for you. The HepVo Waterless P-Trap!

All RVs with holding tanks have a vent pipe secured in the top of the holding tank and going up through the roof, which is where the odor created in the tank is vented. In addition there are the tank inputs coming from the sinks and toilet as well as the shower. To prevent odors from coming into the coach from these devices, other products had to be installed inline, the most common used in the sink and shower drains is the P-trap.

P-trapp-trap diagram

A P-trap uses water in the bottom of it to isolate the coach air from the tank air. You may also have an anti-siphon trap vent device (ASTVD) under the sinks. It is a small ABS plastic device fitting found near the P-traps under the sink. Its purpose is to allow air into the P-traps under that sink, and at the same time prevents sewer gases and odors from coming in from the holding tank and main piping.

astvd vent ASTVD Vent

A typical roof vent prevents water from entering the tank from the vent and in addition creates a venturi action as air passes through the vent cap.

vent cap

There are a variety of different designs for P-traps, ASTVD devices and roof vents, yours may look different from the photos but they all work in principle, the same.

The issue we explore in this blog is the P-trap itself as it relates to RVs.

As shown in the photo above the water in the trap is the isolater between the inside of the holding tank and the inside of the RV. Gases do not leak through water and as a result, it is a simple method currently used almost everywhere. The issue with water P-traps in RVs in particular is the fact that the RV moves and can displace the water breaking the isolation barrier, allowing the gases to come into the living space of the RV.  Another issue is the amount of space a typical P-trap takes up, especially under the shower drain. A lot of RV manufacturers are now using a new device called HepvO, to solve the space issue.

hepvo p-trap diagram           HepVo waterless p-trap

                                 The HepvO is a waterless p-trap!

The HepvO allows water to flow through it, but does not allow it OR sewer gases to go the other way. Simply put, it is a “check valve” of sorts. The product is not a lot bigger than the drain pipe itself , approximatly 7 1/2″ long by 2 7/16″ in diameter maximum. In most cases the standard P-trap can be replaced with the HepvO which comes in two sizes 1 1/4″ and 1 1/2″. The size you would need is determined by the sink down pipe size. The kits come with the most common fittings needed. Addditional fittings, adaptors etc. if needed, can be obtained at a local hardware or plumbing store.

The HepvO valve has been used in most other countries world wide in housing as well as commercial buildings and will be in North America in the future, after plumbing code approval. The product is listed currently and a building inspector can approve its use. The RV Industry’s RVIA has approved its use in RVs.

For more information about the waterless p-trap, go to or call us 877 787-8833 toll free.