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The Bottom Exit Kit Accessory

One of the great advantages of the C-Head is the ability to easily funnel the urine out of the toilet into an outside receptacle such as a black water holding tank like those found in boats and RVs, or an agriculture type storage tank for permaculture use or into a drain field. You can do this using what we call the “bottom exit kit.” In addition to home and cabin installation, this can be done with most RVs, travel trailers and houseboats that have an original, factory installed toilet that flushes into a holding tank through a standard toilet flange that is mounted on the floor. Diverting urine to the holding tank in its concentrated state takes much longer to fill the the tank up and thus significantly extends the time between dumping the tank . In addition, it makes the disposal of urine much easier for both boondockers and for RV and travel trailer owners who prefer to use dump stations. More on that in a minute.

EUD with plumbing to the toilet flange

The system is pretty straight forward. Instead of using a plastic water jug or integrated urine tank (P-tank) for collecting the pee, it is instead shunted down into the black or grey water holding tank using an external urine diverter (EUD) accessory and is then piped into the holding tank using the existing toilet flange.

A 6″ diameter hole must be cut in the bottom of the C-Head housing so that it can sit flat on the floor around the slightly raised lip of the toilet flange. A foam plug is inserted into the flange to seal it off and a P-trap is attached to the underside to prevent the escape of sewer gas from the tank back into the cabin of the RV, the travel trailer or the houseboat. The C-Head, if ordered with the BEX kit, comes with a raised platform inside the housing that the solid waste bucket sits on and which creates a space for the plumbing to run underneath it.

The BEX system can be retrofitted into existing installations of the basic C-Head that are currently using a jug or P-tank to collect urine. It does require the installation of the pedestal inside the housing and either purchasing a new shorter collection bucket from us or else modifying the existing bucket by shortening it. This can be done by cutting off the bottom of the bucket three inches up from the base and installing it inside the top portion. First remove the bucket bar on top and the churn from inside the bucket. Do not remove the lid itself. Once the bottom is cut off, insert the bottom piece inside by turning it sideways and inserting it into the upper portion. This is preferable to removing the lid which is purposefully very difficult to do. The taper of the bucket will allow the bottom to settle inside the bucket where it must be fastened with screws or pop rivets around the sides. The overall height of the bucket from the bottom of the bucket to the top of the lid (not the bucket bar mounted on top) should be held to exactly eleven inches tall. You will also need to fill the gap between the two parts with hot melt glue both inside and out.

In addition, the churn shaft must be shortened by three inches by cutting out a section of the shaft 3 1/8″ and reconnecting the two halves together by gluing the ends into a one-inch diameter PVC connector. You can screw it in place instead if you want to – two screws (4 total) on opposite sides of both halves. If you glue it, work fast and don’t let the glue grab before the parts are fully seated in the connector. Hammer them together using a rubber mallet.

Managing urine with the BEX system is not maintenance free. All urine management systems have to deal with the buildup of scale. The system should be routinely flushed with an anti-scale agent like ZEP acidic toilet bowl cleaner. The system should be disassembled and cleaned annually. Eventually, the hose may need to be replaced but this is simple and inexpensive to do.

Using a BEX kit is especially useful if you are boondocking. By putting only concentrated urine and small, occasional flushes of water into the holding tank, you can empty the tank more easily since you are not dealing with solid waste. A simple modification to the existing drain line cap can be made by cutting a hole in the face of the cap and permanently attaching a garden hose male fitting into it using plumbers epoxy putty. When not in use, the threads of the fitting should be covered with a screw-on thread cap. I prefer to have the female fitting at the cap so that I can back flush the valves and tank. Either male or female will work. After making this modification, I found out that you can buy a cap like this online for around six dollars which is much cheaper than the parts I bought.

RV drain port with hose attachment

To empty the tank, attach a long, dedicated garden hose to this fitting and run it a short distance away from the RV and place the end in a cat hole that is 8-12 inches deep. The urine can be emptied slowly into the cat hole where it will be absorbed and then covered with earth. Attach a ball valve to the hose to control the rate of flow. You can also make a urine diffuser to help disperse the urine and grey water into the cat hole. Read this article (here).

If the ground is not conducive to absorption then the urine can be disposed of at a dump station or transferred to a portable tank such as a marine fuel tank or drain container and then poured into a toilet or carried into the woods to a place where ground absorption is good. The drain hose can be flushed with grey water prior to storage.

Or you can use a portable fuel tank. The urine can be siphoned at a slow rate into a cat hole using a small diameter hose giving the earth time to absorb it. Rinse and allow the tank to dry between uses so that it can double duty as a fuel tank in emergencies.

In cases where the BEX system is being used in boats, particularly houseboats, the urine must be pumped out at a pump-out facility or dumped overboard three miles off shore which is usually impractical for houseboats but not for trawler type vessels. It is rare to find a toilet flange on a sailboat.


Some notes on the nature of disposing of urine. Urine is normally sterile. In my training as an Army Special Forces medic, they advocated using urine in place of sterile water for wound or surgery lavage in field expedient medicine in combat and POW situations. Diseases transmitted by human urine are very rare and usually require that it be diluted in standing water. There is zero danger of transmitting disease or causing an epidemic by disposing of urine using the methods described above. Steps should be taken to prevent urine odor which is a public nuisance. That being said, caution should be exercised that urine is not allowed to get into standing water. The nutrients in urine, while good for vegetation can cause the growth of algae in standing water which can be deadly to existing aquatic wildlife. It is a wide practice for boaters, including the USCG and law enforcement personnel to put their urine in the surrounding water. That is a simple fact. The majority of USCG vessels under 45 feet and run-about law enforcement vessels have no head facilities on board. While dumping urine in the water may not be technically legal it is a law that is flaunted completely by everyone. Bottom line, use good judgement. Disposing of urine is not rocket science but some discretion and common sense is needed.

Please feel free to make constructive comments or ask questions in the comments section below. The products shown can be found online and at local stores. Please note that I am not endorsing any particular brand or vendor of these products unless specifically stated so.

Copyright 2019 – C-Head LLC – All rights reserved.

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