brunnhilde's sanitation system field test

In the last two weeks I went camping trips twice. This give Brunnhilde's newly revamped sanitary system a thorough field tests. My regular readers would recall the major revamp projects are the conversion of the US RV style toilet and black water holding tank back to the European cassette type, and the grey water discharge system that I designed.

My first camping trip consisted of 6 days and nights of "dry-camping" with very little driving. The second trip consisted of 5 days and 6 nights also of "dry-camping" with 120 miles of driving. In both trips I cooked all the meals with supplied I brought from home. I had equivalent of one short shower on both trips (both are windsurfing trips so there is little need for shower except to cool down or wash the soiled hair).

I am very delighted to see how well the electrical, sanitation and fresh water system capacities stand up to isolated camping. I am so impressed how well balanced everything is with respect to the others. The two deep cycle coach batteries supported 72 hours of the cabin use with most of the energy consumed by the Dometic DC refrigerator. By the end of the 72 hours the battery voltage was around 11.8V. With conscientious use of the fresh water tank with cooking and drinking for 1 person the fresh water tank could easily last 4 or 5 days. It could easily last much longer if the meals that I cooked were simpler that involve less holding vessels and washing of the fresh vegetables.

The real life dry-camping shows that the capacity of the fresh water tank, gray water tank, cassette toilet black water caddy, the toilet flush water tank, and the coach batteries are very well sized. They all supports about the same duration of dry-camping and exhausted at about the same time.

The cassette toilet is a pleasure to use. It requires a bit more user mental faculty than the US RV toilet as you have to open the gate valve with the hand lever. The flushing is done by pressing the flush water button instead of just stepping on the foot paddle which opens the gate valve and activate the flush water all in one act. I prefer to open the gate valve before releasing myself instead of leaving the gate valve close and only open it to let the waste drop into the cassette caddy when I am finish. It is important to remember to close the gate valve with the cassette toilet. With the US RV toilet all these is done with one act - step on the foot paddle when you are done. The self-contained flush water holding tank holds more water than you would likely need. When the waste water cassette is nearly full there is still at least a half tank of the flush water left.

Emptying of the waste water was much simpler than the original system which involves the use of the US RV dumping hose (i called it wrestling with the Burmese python). The cassette toilet storage caddy holds about 5 US gallons. When full it is quite heavy (imagine the weight of a 5 gallon paint) and you have to be somewhat fit to left it off from about 4-foot height. For the grey water tank I used a short 1.5-inch diameter hose to drain into the basin of the dump facility. By the second time I realize with most US dump facilities I can simplify the process by using a short rigid discharge adapter pipe instead of bothering with the 1.5-inch diameter hose.

Yesterday I went to home depot to pick up some plumbing parts to fabricate this adapter pipe. To determine  the dimensions I first made a mockup prototype.

more hill billy innovation - my initial prototype with dry-fitting to gauge the optimum lengths

final version - the total length is designed so it would fit into the tray that i store the 10-foot dumping hose and fresh water hose

With the rigid discharge adapter pipe all I have to do is drive up next to the dumping basin, slip on the discharge adapter pipe and open the red valve. Once the tank is empty the rigid adapter pipe is very easy to rinse clean.

it takes up no more room to store as it take advantage of the dead space in the plastic tub that I store the hoses

Since the cassette toilet conversion I no longer have sewer gas problem when camping or parked. The only time I can smell sewer gas is when driving with the front window(s) open. This clearly points to the reversed pressure differential when the vehicle is moving with the front (window(s) open. I decided to experiment with my enhance roof vent for the sewer gas. I picked up two ABS plumbing fittings so I may figure out how to improve upon the sewer gas vent.

two ABS plumbing fittings for the experiment - a 90-degree elbow and a t-fitting

first version

second version

i decide the first version using a t-fitting make more sense to create a suction when the vehicle is in motion; this arrangement works like a vacuum pump driven by compressed air

Some reader would point out there are RV products that are designed just to do this so why am I re-inventing the wheel. I have researched and reviewed them and to me they are poorly design and made. Their over-promised claims sound good for simpletons. For someone who has some mechanical amplitude I know they are mostly junk and I rather save the money for a few pints. My version cost less than $2 and will last much longer in the elements.

This morning I went out for a drive to make sure my design does not create a loud whistle at highway speed. All is well even when I open the front window(s). I could not hear any whistle sound. Unfortunately the waster water tanks are quite empty so I cannot determine the effectiveness of my (rather preliminary) design. I will have to wait until the waste water storage tanks have a potent brew to be able to tell if this solves or reduce the odor. With this design I can perform some additional tuning to encourage the suction based on simple aerodynamic theory that air stream travel along the longer surface has lower pressure than the one along a shorter path.