Grey (gray) Tank won't drain!

[Cdok1]

Model: 2004 Bigfoot 30MH29SL Class-C RV on a Ford E-450 chassis
Went to dump station, after 2 days use to drop the grey tank and just a trickle of water came out! The time before, we used too much water and the shower/bath had backed up, though that time 2 days prior the grey tank drained well.

My first thought was the waste valve was not opening, the handle no longer connected to the plate. So, I removed the drain valve and still nothing came out. The valve is fine. Fun work roadside at a county park and we needed the water out!

It was getting late now, so my next thought was to drive it down a bumpy stretch of road with the drain valve open. Not to offend our environmentally concerned readers, but this was an emergency! It worked, as I laid trail of water down the stretch of an Arizona backroad, water coming out more when accelerating and/or cornering.

After we returned home, I tried to snake the drain. My ¼” snake with a wider head made the first two 90 degree turns in the drain, but not the 3rd which is the turn up into the tank. I removed the bath vent valve and tried to snake the vent entrance down into the top of the tank. Same issue, the snake did not reach the tank.

I ordered a “Camco Dual Flush Pro Holding Tank Rinser with Gate Valve” on Amazon and that also did not work. I have a gallon counter and pushed 14 gallons up into the tank and maybe 2-3 gallons came out.

On another day, I connected my clean hose to the water supply, filled the hot water heater and emptied it all in the tub. The hot water drained nicely down the tub drain, but nothing came out the tank drain valve.

So, I again removed the grey tank drain valve. I bought a high-volume hose nozzle, with a cone-shaped end, that fits nicely and fully into the opening of the 1 ½” ID drainpipe. I ran water up the drain and in about 10 seconds I could feel and hear that the drain was full, with water pushing up into the tank, a good 3-4 gallons worth. Then I turned off the hose, released and all that came out was about a quart of water, the amount of volume in the drain piping and nothing more. I did this 4 times to no avail!

Next, I fed the hose up by the bath p-trap. Believe it or not, there is a wide opening around the p-trap (no insulation here) and with the service panel off you can pull the hose up into your bedroom! I then forced water down the vent behind the bathtub. Pushing a good 2 gallons worth twice, no water entered the tub or came out of the tank with the tank drain still wide open.

With all this, I now have 20+ gallons of water in my tank. The drain is still wide open and not a drop. It's like my tank drain has a built-in backflow valve! And I'm pretty sure if I drive it down the road it will come out. I’m looking forward to hearing your feedback. In doing so, please keep in mind all that I’ve tried so far. Thank you –

[DamonCamper]

Following

[Weeds636]

https://www.harborfreight.com/automo...era-64623.html

You may need to purchase one of these to see into the tank.

[Cdok1]

Originally Posted by Weeds636

https://www.harborfreight.com/automo...era-64623.html

You may need to purchase one of these to see into the tank.

Thanks Weeds, says this scope is 38" long and either the length or the 3 turns may keep this from getting into the tank. I'll keep this in mind, though I'm hoping for someone to comment who had a similar experience.

[Ron Dittmer]

This is a long shot, but I wonder if the round remnant when the tank was drilled for the pipes, was not removed......maybe still attached by a thread of plastic, acting like a check valve.

[THenne1713]

Originally Posted by Cdok1

Model: 2004 Bigfoot 30MH29SL Class-C RV on a Ford E-450 chassis
Went to dump station, after 2 days use to drop the grey tank and just a trickle of water came out! The time before, we used too much water and the shower/bath had backed up, though that time 2 days prior the grey tank drained well.

My first thought was the waste valve was not opening, the handle no longer connected to the plate. So, I removed the drain valve and still nothing came out. The valve is fine. Fun work roadside at a county park and we needed the water out!

It was getting late now, so my next thought was to drive it down a bumpy stretch of road with the drain valve open. Not to offend our environmentally concerned readers, but this was an emergency! It worked, as I laid trail of water down the stretch of an Arizona backroad, water coming out more when accelerating and/or cornering.

After we returned home, I tried to snake the drain. My ¼” snake with a wider head made the first two 90 degree turns in the drain, but not the 3rd which is the turn up into the tank. I removed the bath vent valve and tried to snake the vent entrance down into the top of the tank. Same issue, the snake did not reach the tank.

I ordered a “Camco Dual Flush Pro Holding Tank Rinser with Gate Valve” on Amazon and that also did not work. I have a gallon counter and pushed 14 gallons up into the tank and maybe 2-3 gallons came out.

On another day, I connected my clean hose to the water supply, filled the hot water heater and emptied it all in the tub. The hot water drained nicely down the tub drain, but nothing came out the tank drain valve.

So, I again removed the grey tank drain valve. I bought a high-volume hose nozzle, with a cone-shaped end, that fits nicely and fully into the opening of the 1 ½” ID drainpipe. I ran water up the drain and in about 10 seconds I could feel and hear that the drain was full, with water pushing up into the tank, a good 3-4 gallons worth. Then I turned off the hose, released and all that came out was about a quart of water, the amount of volume in the drain piping and nothing more. I did this 4 times to no avail!

Next, I fed the hose up by the bath p-trap. Believe it or not, there is a wide opening around the p-trap (no insulation here) and with the service panel off you can pull the hose up into your bedroom! I then forced water down the vent behind the bathtub. Pushing a good 2 gallons worth twice, no water entered the tub or came out of the tank with the tank drain still wide open.

With all this, I now have 20+ gallons of water in my tank. The drain is still wide open and not a drop. It's like my tank drain has a built-in backflow valve! And I'm pretty sure if I drive it down the road it will come out. I’m looking forward to hearing your feedback. In doing so, please keep in mind all that I’ve tried so far. Thank you –

I have (read of several cases) where owner found tank cutout from drain connection was not removed from tank, and worked its way into being a blockage? Sounds like your issue, or kids dropped something into plumbing?
You can probably search this site and find similar tales? BEST resolution sounds like after finally draining tank. disconnect, drop and inspect up close. RUBBER drain COUPLINGS w/ HOSE CLAMPS can be a god-send for cut pipes vs glue joints, quick, easy and reliable, also adding some flexibility and future access?
- MY closest comparison is when the GATE came off a check valve (plastic hinge broke after 15yrs) in sump pump line, pump running but nothing coming out of discharge.
- My best SUGGESTION is push garden hose up into tank, it may push plastic plug out out the way enough for water to drain thru the hose itself?

[tarnold]

Got an air compressor? Crank up the pressure, using a “wand” with an air control valve(blow gun)stick it in the top or bottom of the run(blow up or down) Use a rag to seal around the wand as best you can. Start off with short blasts. Have someone at the other end to see what comes out.

[MrMark52]

I don’t think I would use compressed air, or at least anything over 5-10 psi. I can see busted pipes or ruptured tank in your future if things go awry.

Maybe try to do the same with a wet-dry shop vac. You could apply pressure or pull suction on the tank, and it might be easier to make the hose to piping transition. Maybe the vacuum can pull liquid past the blockage so as to drain the tank and make things easier to inspect using a usb camera hooked to your computer (can’t see much when tank is full of water unless you get a true plumbers camera).
I bought a USB IP67 (or 8) camera off of eBay or Amazon fairly cheap several years ago that would be perfect for snooping around the inside of your system to see what is causing the problem.
You can go up the discharge pipe, or through a drain or roof vent with it.

[tarnold]

You blow out 1/2” water lines with a compressor. Wouldnt think a 3” pipe would suffer.

[MrMark52]

Originally Posted by tarnold

You blow out 1/2” water lines with a compressor. Wouldnt think a 3” pipe would suffer.

Water lines are designed for upwards of 80 psi (my rusty memory is saying 125 but I wouldn’t go there).

Waste piping isn’t rated for that pressure as it only see’s the weight of the water. Go look at your PVC fittings at the local hardware store - pressure fittings are heavier and have a deeper insertion fit as opposed to PVC DWV (Drain Waste - Vent) fittings.
Note that the pipe is marked accordingly for either 125psi or DWV.

[bigb56]

There might be something solid in there that's loose enough to move around but too big to fit thru the drain and keeps rolling against the outlet. I can't imagine what, or how it got there, maybe a circle cutout which has been suggested but that would mean it's been in there for 18 years.
As an example I once had an auxiliary fuel tank with a straight 3/8" pickup out the side with no sock or screen and I kept running out of fuel on that tank, later found out there was a tiny ball in there that would roll up against the pickup and cause the truck to run out of fuel.
Will be interesting to see what you find.

[RoadTrip2084]

When this has happened to me in the past I use this method to clear any obstructions and it has always worked:

1. Attach your dump hose to the fitting and connect to the sewer/dump station.
2. Assuming at least a trickle will drain when you open the drain valve, open the drain, letting the hose fill as completely as possible. While filling raise the middle section of the hose above the tank drain height so that it acts like a tank and fills as completely as possible
3. Now rhythmically and rapidly lower and raise the body of the hose, without letting it drain out the sewer side. This will create a pressure wave going back to the tank drain hole and will cause a large backwash of grey water into the tank, generally pushing any obstructions in the drain out and away from the hole.
4. At the top of one lower/raise cycle drop the hose quickly to the ground.
5. The grey tank should now be draining at full pressure/speed.

Here's a video showing the technique:

https://www.youtube.com/watch?v=BUmPMGDEKxY

[DerekF]

Maybe try something like this

https://www.irv2.com/forums/f278/gray-black-tank-super-enema-568838-4.html#post6077701

[znt1186]

If properly installed and functioning , waste holding tanks have a vent out the roof of the rv. No pressure should build up in a properly operating system. Even with a malfunctioning vent, pressure should blow through the p traps and be relieved that way. A borescope with a longer camera feed might be able to scope the tank for you. If you can't get one to do that, you might try a local plumbing company with a camera. Otherwise, if you can get a piece of fairly stiff tubing forced up through the opening, it may indicate if there is a blockage at the drain inlet.