ATF: Mallard - Blackwater Flush - Procedure vs Leaking

[PeterS]

Good Morning,

The printed instructions (and online references) mostly suggest to hook up the black water flush with the valve CLOSED and add about 5G of water, then open the valve to rinse out.

The sticker at the BW flush states to leave the valve OPEN. This does not clean very well however.

1. What is the BEST/PROPER BW flush procedure?

2. When using the first method (closed, 5G) we start to see water dripping from underneath the underbody in the kitchen area, suggesting a leak. (CW was unable to replicate as always). Is this a cause for concern?

 

[BigJim45]

Good Morning,

The printed instructions (and online references) mostly suggest to hook up the black water flush with the valve CLOSED and add about 5G of water, then open the valve to rinse out.

The sticker at the BW flush states to leave the valve OPEN. This does not clean very well however.

1. What is the BEST/PROPER BW flush procedure?

2. When using the first method (closed, 5G) we start to see water dripping from underneath the underbody in the kitchen area, suggesting a leak. (CW was unable to replicate as always). Is this a cause for concern?

This is just what I do.....empty black tank.....hook up hose to flush black tank.....turn on water to flush black tank......turn off water after about 10 minutes......I keep valve open at all times.

As far as your leak.....you may have a bad check valve.

 

[PeterS]

Txs. How do I check the "check valve" - is there a way to access plumbing without removing the underbody cover ?

 

[JohnDar]

If you're getting a leak while running water into the black tank flush system, it's possible there is a loose hose connection or the cheap anti-siphon valve has broken. Mine did that and I had water running inside the rig.That valve is located somewhere in a wall cavity above the toilet. Or it might be behind the round access port in your shower stall. Supposedly, there is a check valve in the hose connection for the tank flush, but mine was just a plastic flow restrictor. When it broke, I installed a real check valve. If your tank has been dumped and you're running 5 gallons back in (for sure that's all), there should not be a leak if the system is intact.

When I dump, I open the sewer valve and then turn on the flush and let it run. Occasionally, the flow out the sewer may stop due to some blockage, but eventually it gushes out again pushing the blockage with it. That said, I keep an eye on how long the flow has stopped and how many gallons I've put in (I have a water meter on my system). If it seems that it's really blocked, I hook up the hose to the backflush connection on my sewer outlet adapter and push it back. Have not had a problem with it not doing the job.

Once satisfied that I've dumped all that's coming out, I close the black tank valve and run 5 or 6 gallons of water into the tank via the flusher, again, watching the meter. Then I go inside and dump a 2 gallon bucket of water into the toilet with some Calgon added to it. You ALWAYS want to add some water back to the tank after dumping before using the toilet again.

 

[danemayer]

Hi Peter,

Before you go too far hunting for possible leaks, let's back up a bit.

If your tank needs to be dumped because it's full, keeping the valve closed and adding 5 gallons of water will cause the tank to expand, which will stress connections and can force water out.

So I would do a reset.

A general procedure is to:

1. Empty the black tank
2. Close the gate valve
3. Add water through the black tank flush fitting, using a timer on your smart phone so you don't overfill the tank. You'll need to know the capacity of your black tank, and the approximate water flow from the hose. I'd suggest filling 50-60% based on time. So if you have a 30 gallon black tank, and a flow rate of 5 gallons per minute, you'd fill it for 3-4 minutes to put in 15-20 gallons.
   NEVER WALK AWAY OR GET ENGAGED IN A CONVERSATION WHILE USING THE BLACK TANK FLUSH, WITH THE GATE VALVE CLOSED.
4. Turn off the water.
5. Open the gate valve to empty the black tank again.
6. Repeat steps 2-5 to dump a 3rd time.
7. Close the black tank gate valve
8. Add about 5 gallons back to the black tank so as you use the toilet, the solids land in water.
9. Open the kitchen gray valve and dump that tank.
10. Close that valve.
11. Open the bathroom gray valve and dump that tank.
12. Close that valve.

At that point your sewer hose should be relatively clean.

If you still have a leak, as mentioned, it could be the anti-siphon valve which is probably behind the shower knobs. You may or may not have an access panel. You could determine if that valve is leaking by opening the black tank valve and running the black tank flush for an extended period.

If you haven't seen our owner-written Water Systems Guide, that may have additional information that you might find helpful.

 

[PeterS]

Thank you for your extensive response. Those are pretty much the processes I am following when emptying the tanks. I have yet to overfill one
(And I have read the HUG manuals as well.)

I also have a water meter on the hose to properly gauge the amount of water I am adding thru the blackflush system.

The leaking begins a while after the black tank is empty, gate valve closed and I use the backflush for an about 5G fill. It does not stop whether the gate valve is open or closed, just seems to take time to accumulate.

I know there is an access panel under the shower/tub - how can I identify or troubleshoot the anti-siphon valve if that is the next step?

 

[danemayer]

I know there is an access panel under the shower/tub - how can I identify or troubleshoot the anti-siphon valve if that is the next step?

Here's a picture from a Bighorn where it's located by the PEX lines to the shower. I don't know if Mallards use the same location. You may be able to follow the PEX line from the black flush fitting to get an idea where to look.

 

[Chopperno1]

Here's a picture from a Bighorn where it's located by the PEX lines to the shower. I don't know if Mallards use the same location. You may be able to follow the PEX line from the black flush fitting to get an idea where to look.

View attachment 51108

The valve in the picture above is under bathroom sink on the m32.

 

[PeterS]

Thank you. Then I believe my leaking issue cannot be there, as I have no water in the bathroom or under the sink.

Where/what should I check next ?

 

[Rychehawk]

Thank you. Then I believe my leaking issue cannot be there, as I have no water in the bathroom or under the sink.

Where/what should I check next ?

I have an M29 but I think the black tank flush connection is in the same location or the same type. Mine is on the right side of the of the coach opposite the tank valves. I am not sure what it looks like but I would think to look at the plumbing that connects the flush port to the black tank. It could simply have a leak in one of the joints/connections.

good luck

 

[PeterS]

Update Nov '17:
Thanks to Hurricane Harvey, we had the underbelly completely restored and during that time had the shop check and tighten all connections on the black tank flush system in the underbelly. Tested it heavily a couple of weeks ago and ZERO leaks.
Clearly, some thing was loose that CW's service failed to fix (or spend the time on, given the sealed underbelly).
Just happy it finally works as intended.

 

[cookie]

Thanks for the update. Good to hear that the leak is finally gone.

Peace
Dave