While waiting for the key parts to arrive for the project, I examined a range of design ideas of the orientation of the tank, as well as finding the optimum plumbing fixtures. As I really dug into all the options there are so many way to accomplish the end. Like the saying, there are many ways to skin a cat.
I browsed through all the plastic plumbing fittings that West Marine has to offer. I found some that are potential candidates. I wanted to test out the tank for leak, as well as to see how much bulging the side walls undergo when filled with water. I have to take a trip to Home Depot to pick up a few fittings. While I was there I went through a few categories of plumbing fittings to find all the viable parts for the project.
the PVC fittings for household fresh water application
i also looked at if anything suitable in the hydronic heating section - this plastic tubing loop may be useful for the breather and overfill port tubing
learnt something new - the hose barbs for PEX tubing has much smaller diameters than common hose barbs because the PEX hose hardly stretches
i picked up these two 1/2" NTP male to 5/8" barb
i ended up using it to plug the rear cabin water heater that i decommissioned - i didn't feel like crawling under the vehicle to struggle with the forest of hoses and to be doused with coolant fluid; i had to take another trip to Home Depot
i pick up a 4" deck plate for the tanks access port - it will serves to install and service the Comet VIP plus pump as well as gravity filling the tank when the rare situation requires
i closely examine the design and construction of the deck plate; the plastic parts are very good quality though I would like them to be of heaver construction; this part is not for used below water line
the o-ring cross section diameter is a bit thin to my liking; there are also some molding squeeze out that i initially was concern could interfere the o-ring forming good seal with the plastic surface
i deliberately pushed the lid hard toward one side - you can see the largest gap is at 4 o'clock
i pushed it to the opposite side - the largest gap is now at 10 o'clock; examined the plastic lid mating surface with the o-ring i decided this should not negate the function for my application since the deck plate will be install on the top surface of the tank
i chose the deck plate that has the diamond non-skid pattern instead of the smooth one out of cosmetic preference
it was a scorching 90-degree F day so i waited until 9 pm to test the tank; i brough home a huge assortment of plumbing fittings no knowing which ones i would eventually use
as one of my goal is to avoid the need to create new ports on the side i am entertaining using the lower 1/2" port for filling, and for draining; i patched in a Gardiner male quick connect fitting
i note the apex of the strengthening creased cross hatch before filling the tank
there is only slight increase of bulging - but with higher temperature i expect it to bulge more; however by laying the tank flat the sides bulges much less than orient this tank as the design intended with it tall and skinny
this is as high as one can fill the tank - there is about an inch of air inside
i try to figure out the best plumbing arrangement for this rearward point port installation
as you can see i have to find fittings that hug tightly close to the tank
since there must be a valve to close the port once the pressure forced filling is complete i grab my Gardiner valve; i was considering buying a garden variety 1/2" PVC valve but dislike the turning friction; the Gardiner is butter smooth and has very little turning resistance
I could not find a satisfactory way to address the overflow and breath port in the port facing the back orientation of the tank. Since there will be a lot of situations the water will overflow from the overfill port I need to route the tubing out of the vehicle, the port facing rear configuration just does not work. I went back to my original idea of having the ports facing forward.
Everything begins to fall into places once I figure out how to address the filling and draining with the ports facing forward. I just need to have a short segment of say 1/2" or 5/8" hose that I can extend out of the back door (for filling and draining). The hole left by the dumping port of the old black tank is perfect for the overfill and breather tube. I don't have to drill a new hole in the floor for this.
the square hole on the floor used to the dump port for the old black tank (i patched up with fiberglass); i just need to drill a small hole to pass a 3/8" tube
there is even a "hanger" for the breather/overfill tube - at the red arrow
a mockup with a short hose for the filling/draining port - filling and store position
draining position
Next I wanted to verify my assertion that I can repurpose the flush water line of the old toilet. This test that I rigged up will allow me to verify two important things. The primary pump already has a non-return valve somewhere, and that his tubing provides enough flow for the axillary tank to feed all the internal faucet (hot and cold). I rigged up my cheap spare pump for this experiment.
for this test i just use a power supply to power the pump
i need to prevent the primary pump from running when I turn on the facets; i pulled the fuse, but then i remember there is the pump inhibit switch already there
Even with the cheap pump there is no lack of flow or pressure at all the facets, both hot and cold. It is important to check the hot water path as it has more resistance than the cold path. I also let the pump run with all the facets closed, to see if the water is pumped into the primary tank. All is good and the non-return valve is doing the job.
this cheap pump empty the bucket of water in no time; it is just a noisy pump and you can just tell it has lousy bearing and will not last at all
At this point I am very comfortable with my conceptual design of this convertible auxiliary tank. There is minimal modification of Brunnhilde at all. No need to add any new hose routing to the cabin interior nor to the side of the vehicle as I originally envision of converting one of the utility ports for filling. There is just very simple wiring of adding a pump selection switch of which tank to draw water from. I already have an idea for the location of this switch. I will repurpose the pump inhibit switch Westfalia provided. I will replace it with a 3-position SPDT center-off switch. That means I only need to run one wire from the new tank to the switch and replace the switch. The best part of this auxiliary tank it is convertible in that I can remove it, without the use of any tool, to free up the space for cargo. The project also involves no new holes to be drilled, except for fasteners to secure the tank. I don't even have to add a new fuse for the auxiliary water pump.
When I first removed the old toilet and replace it with the cassette toilet with self-contain flush water and pump, I was expecting someday I will find a use for the cold water feed from the primary pump. Here I am almost a year later that hose that I capped is now repurposed. When I first set out to restore the cassette toilet as Westfalia intended originally, I did not anticipate the space saved from ridding of the black water tank would lead to so many untapped possibilities.
I have gave some thought to the location of the pump in the auxiliary tank. To increase the likelihood of the pump picking up the most of the last bit of water dead center of the tank is optimum. However if you consider often one stopped on a roadside pavement then center of fore-aft and slightly right biased is ideal to account for the drainage of the roadway.
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