Black Water won't drain, all tanks gasp for air.

Folks, I have an issue with my Black tank draining (might be valve) but lately I noticed when draining all tanks, the water runs for a bit then it seems to stop for a second or two and I can hearing a sucking sound in the hose. Seems to be gasping for air from the dump station. Should there not be an ample supply of air from the roof vents to allow easy drain of tanks?

Might be time to get on roof and inspect vents.

Oregon_Camper said:

Might be time to get on roof and inspect vents.

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Thank you sir. I was pretty sure that would be the outcome. Just too old to get up there so I'll get neighbour to help. Do the rain caps just twist off?

monster007 said:

Thank you sir. I was pretty sure that would be the outcome. Just too old to get up there so I'll get neighbour to help. Do the rain caps just twist off?

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Until you can remove the cap and inspect it (there is a screw in the top under caulking), you could hold the toilet flush open while dumping the tank to allow air into it. There have been reports at times of owners finding the vent pipe has somehow dropped down and the end is under liquid.

monster007 said:

Folks, I have an issue with my Black tank draining (might be valve) but lately I noticed when draining all tanks, the water runs for a bit then it seems to stop for a second or two and I can hearing a sucking sound in the hose. Seems to be gasping for air from the dump station. Should there not be an ample supply of air from the roof vents to allow easy drain of tanks?

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Where are you dumping? Same spot all the time. I am questioning if our septic system needs pumping or if roof vent is the issue? Chris

SNOKING said:

Where are you dumping? Same spot all the time. I am questioning if our septic system needs pumping or if roof vent is the issue? Chris

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Thanks for the reply. Yes same spot. Its parked at an RV Resort. The system is actually a huge holding tank which gets emptied every Monday. We are too close to a river for a septic field. I seem to be the only one having this symptom but not to say there isn't an issue the draining system.

Two issues here. My more serious issue seems to be the Black isn't holding liquids. I know gauges are far from perfect, but I can to to bed at night it may read 3/4 but in morning down to 1/4.

Then at end of last weekend I drained it (was not the usual massive swooshing noise), rinsed it with built in tank flush. Then closed it, filled it with water now I can't seem to get it drained. Im thinking may the rubber seal of the valve moved and blocked it open to begin with but now I wonder if its a vapour lock stopping it from draining ? We do have a problem with Bats living in places like the back of refrigirater so i wonder if they've nested in sewer vents.

I am guessing that if your black tank does not hold liquids, you might have a larger mess that you think. Black tanks need lots of liquid to drain properly. It is possible that a plastic cutout from the black tank is blocking the valve.
Do you have a clear fitting that attaches to the drain? This way you can see I anything is leaking past the valve.

If you have anything living behind your fridge, you need to put screens on the vents. Screens will reduce air flow a bit but this is fixed with additional fans. ( see youtube ).

monster007 said:

Then at end of last weekend I drained it (was not the usual massive swooshing noise), rinsed it with built in tank flush. Then closed it, filled it with water now I can't seem to get it drained. Im thinking may the rubber seal of the valve moved and blocked it open to begin with but now I wonder if its a vapour lock stopping it from draining ?.

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Seems like this happens to a lot of folks to a point..including myself.

I found that by adding this aftermarket valve and then using the grey water to backfill the black tank really really really helps.

Steps:

1 - Install this valve at the end of current dump valve (30 second job)
2 - Drain black tank and rinse with tank flush (built into trailer)
3 - Close this valve
4 - With grey tank full, open grey tank and black tank. Water from grey will be forced into black.
5 - Listen for water to stop flowing (equalizes)
6 - Close grey tank valve
7 - Open new valve and be amazed at what still comes out of black tank. (assuming you have the clear elbow installed)

Link to Amazon



Link to Clear Elbow on Amazon

If the black tank gate valve is leaking water, then you have a mess inside the black tank. When last you dumped it, you probably got a little bit out by running water through the black tank flush. There's probably a bunch of solid waste in the tank and it's likely blocking the opening.

Get a clear sewer outlet adapter with a backflush fitting. Or get a combo that includes an external gate valve. Or, if you get a clear adapter with backflush, but no gate valve, place a separate twist-on gate valve after the clear adapter. Close the gate valve and attach a hose to the backflush fitting on the clear adapter. Run water for 60-90 seconds to push the blockage away from the black tank valve. Then turn off the water to the backflush fitting and see if you get a bunch of stuff coming out the sewer.

If that helps, then after it stops draining again, close the external gate valve and run the regular black tank flush for 6 minutes (timing on your phone). Dump the tank again. Use the clear adapter's backflush fitting if necessary to dislodge any additional black tank valve blockages.

Repeat the fill and dump cycle 3 or 4 or 5 times until everything is out of the black tank.

Gary521 said:

I am guessing that if your black tank does not hold liquids, you might have a larger mess that you think. Black tanks need lots of liquid to drain properly. It is possible that a plastic cutout from the black tank is blocking the valve.
Do you have a clear fitting that attaches to the drain? This way you can see I anything is leaking past the valve.

If you have anything living behind your fridge, you need to put screens on the vents. Screens will reduce air flow a bit but this is fixed with additional fans. ( see youtube ).

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Thanks. (I think). Words an RV owner never want to hear. Have already screened the fridge so thats dealt with but I will check the roof vents this weekend. Yes I have clear fitting and external valve. Bought them yesterday.

Also I'll drop the corplast and look at cable. Someone suggested they can kink and not operate valve completely. If I can get it draining I'll install an external valve for now. Season ends Sept 23 for us so might be spring before I get it all apart.

Here is the routine I have developed over many snowbird winters.

1. Get a clear sight adapter and put it between the trailer and the sewer hose.
2. I leave the black tank closed for a week at a time. Grey tanks open.
3. I form a pee trap in the sewer hose with a couple boards, one 2x and a 4x4.
4. To dump and flush, I remove the pee trap boards.
5. Close the grey water tanks.
6. Open the black water tank and turn on the hose to the built in flush system.
7. Watch the sight tube until I am down to just hose water coming out.
8. Go inside and do two full bowl super flushes. "Bomb the Pile!" Note: Full bowl means filling the bowl to the bottom of the upper rim.
9. Go back outside and view discharge.
10. Close the black water tank and run the flush water in for four(4) minutes. Do not let anyone distract you at this point.
11. Open and drain and repeat 10 again.
12. Flush a bit and verify that you have nice clear water coming out of the tank. If not go back to step 8 and start again.
13. When you have nice clear discharge, put the pee trap boards back the sewer line and fill the pee trap.
14. Close the black water tank and add about a minute worth of water to the tank with the flush hose.
15. Secure the flush hose. I have a little inline valve adapter at the side of the trailer and the other end gets turned off.
16. Open the grey water tanks and go add your chemical to the tank.

I have had the burping a couple of times, however the super flushes seem to have fixed that issue.

Having piles in not good!!

Chris

monster007 said:

Folks, I have an issue with my Black tank draining (might be valve) but lately I noticed when draining all tanks, the water runs for a bit then it seems to stop for a second or two and I can hearing a sucking sound in the hose. Seems to be gasping for air from the dump station. Should there not be an ample supply of air from the roof vents to allow easy drain of tanks?

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Folks, thank you all for your help. I got it working. The one piece of advice that really works is having a clear piece on the drain tank so you can watch to see when your all clear.
Thanks again!