DIY: City Water Manifold (and my process for dumping the black tank)

I’m really thankful that my coach came equipped with a black-tank-flush system.  I use it religiously each and every time I dump the black tank.  It takes quite a while for the two of us to fill the black tank (and I only dump it once it is full to ensure a good “flush” of the contents), so even though it can be somewhat time-consuming, it only happens once every 2-3 weeks.  What I don’t like is the process of attaching a separate hose from the black-tank-flush connection directly to the city water spigot.  It doesn’t seem like much, but depending on the situation, that can be the hardest part of the entire process (like if the bay door is blocked from fully opening by a tree or power pedestal).  It also means that I have to carry a dedicated hose just for this purpose.

I’m sure that some are wondering, so here is my process for dumping the black tank:

1. A day or two before; close the gray tank, if it has been open, to fill up the gray tank.
2. Attach my black-tank-flush hose (I’ve elimitated this with my new manifold).
3. Open the black tank valve and empty the contents.
4. While the tank is draining, turn on my black-tank-flush.
5. Wait until I have only the stream of clear water coming out that I can assume is the black-tank-flush water. (A clear elbow is basically a necessity for this entire process)
6. Close the black tank valve.
7. Allow the black tank to fill to at least 2/3 full – BE VERY CAREFUL TO NOT OVERFILL
8. Again, drain the black tank until it is only a trickle of clear water.  You will likely see quite a bit of “debris” on this second draining.
9. Fill the black tank again to at least 2/3 full.
10. For a third time, drain the black tank.  This time should be mostly clear water.
11. If the last step still had more than a small amount of solids, repeat the fill and dump process until it is just water.
12. FINAL STEP: Empty the gray tank to rinse out the sewer hose.

I realize a lot of RV’ers let the black-tank-flush run until they have clear water coming out of the tank and call it a day.  I think the first time you do a second flush, using city water, you’ll realize that your tank still has quite a bit of “stuff” left in it.  An awesome series of videos from The Fit RV using a clear tank for deomonstration will help to show just how much is left after the initial dump.

Alrighty, now that we got all of that out of the way, I can tell you the solution that I came up with to make this process much quicker and easier!  I created a city water manifold system which can divert my city water source to the black-tank-flush system with the quick flip of a valve.  No more getting out my dedicated black-tank-garden-hose, hooking it up, draining it, and packing it back up!

I certainly didn’t make up the idea of creating a water manifold in the wet bay.  I’ve seen various versions of this; some more elaborate than others.  I started off making mine out of PVC pipe.  I am not against this idea, but I felt like there was an easier way.  So I returned all the PVC fittings that I had purchased (they were never used) and began looking at PEX tubing. For those who aren’t familiar, PEX is the tubing that is likely running through your RV right now – and/or your house.  I really liked the idea of having flexible tubing, versus rigid pipes, but I was having considerable trouble easily sourcing the various fittings and adapters that I would need to make it work.  So then I thought “Let’s really dumb this down.  I already use garden hose and garden hose threads, so why change it!?!”.   So far, it’s been working great!

Let’s go through what you’ll need to make your own!

• Drinking-Water Garden Hose
  • This is not what is hooked to your water source – this will be cut up to use as pieces in your manifold
  • I went with 5/8″ inner diameter, but you can use any size you’d like.
  • I bought a 25 foot Camco hose and it was less than $10. You’ll really only need a couple feet.
• Hose-Repair Kits
  • These are replacement ends for a garden hose
  • You will need 3 male and 3 female in total, but you can use one of each from the hose you’re going to hack up
  • I tried two versions with equal success: one kind uses a traditional hose clamp to hold the barbed threads to the hose and the other uses a larger metal clamp designed specifically for this application.
  • Make sure you buy the correct size for the inner diameter hose you’re using
• Garden Hose Splitter (also called a “Y”)
  • These can be found at many different places.
  • Go with a brass unit over plastic since this is used with drinking water
• Garden Hose Vacuum Breaker (2 of them)
  • These are used as check valves to prevent back flow of water
• 90 Degree Hose Elbow (2 of them)
  • This was needed for my application, but depending on design, your wet bay may not need them
  • Again, use brass versus plastic
• Pressure Regulator
  • Many people will already have this and some folks don’t use one at all
  • I am using a Watts whole-house pressure regulator that was adapted for use with garden hose threads , and a pressure meter, from RV Water Filter Store
• Inline Hose Valve (Optional)
  • I added this for peace of mind – you’ll read why down below

Let’s put it together!!

1.  Attach the 90 degree elbows to your city water and black-tank-flush connections, if necessary.
2. Attach a vacuum breaker to each elbow.
3. Create two small hoses to connect the vacuum breakers to the female side of your splitter.
   1. If you’re using the optional inline valve, place it in your black-tank-flush line.
4. Either hook up your pressure regulator directly to your splitter or create a hose to run to your pressure regulator.

That’s basically it!  You’ll want to double check to make sure that all of your hose-repair-kit connections aren’t leaking.  If they are, tighten them down further.

To use the system, you’ll connect your main water hose from the city water source to your pressure regulator.  Then you can use the valves that are built into your splitter to control where that water is flowing.

Before I get blasted by the germ-a-phobes out there, I realize that this isn’t for everyone.  I don’t see how the two systems would contaminate each other, but the thought alone may be too much for some folks.  Using the vacuum breakers on not only the black tank side, but also on the city water side, there is no chance of water flowing backwards to the splitter.  I will also add that you would never have both sides flowing at the same time.  When I travel, both sides are shut off.  When one is in use, the other is turned off.  For black-tank-contaminated water to mix with your drinking water, the water would have to fight gravity and be sucked back to the black-tank-flush connection.  Then it would have to somehow bypass the vacuum breaker, go to the splitter and both valves would have to be open.  I honestly don’t see how this would be possible, but that’s what would have to happen.

On the parts list, I mentioned a secondary, inline valve.  For me, I’m not worried about the contamination risk, but I do think about what would happen if the valve on the black tank side was to fail.  If that was to happen, water would be pumping into the black tank, via the black-tank-flush, and I would have no idea until something awful happened.  Now, the chance of that valve failing in the splitter is extremely minimal, but the consequences are so great that I decided to double up and add a second valve.  With this setup, two valves would have to fail, at the same time, before I would have black water flowing OUT of the toilet.

OK, that’s what I’ve got for today!  This is a very easy and fairly inexpensive project that anyone should be able to do.  It’s great on days when I flush the black tank.  All I have to do is turn off the city water side and turn on the black tank side – super simple, quick, and easy. When I’m done flushing, I just flip them back the way they were when I started.  If you have any suggestions on how I could improve upon my design, I’m all ears!  Just comment below or Contact Us!

See you on the road,

Ryan, Kim and Jet