3 inch grey water drain?

[1Longbow]

As I have posted on here ,we are having a problem with our grey water tank draining. It really takes about 35 minutes to drain the tank. I have pulled the drain pipe and washed out the tank and could find nothing plugged. The drain pipe is 1 1/2 inches in diameter. Would putting a larger diameter drain pipe help,or should I be looking somewhere else. I put a new vent cap on,but right now I'm at wits end,trying to figure this out. I don't want to put everything back together until I have exhausted all the options. gate valve works just fine. Any ideas or suggestions? Thanks to all of you.

[1Longbow]

Well ,I replaced all the grey water plumbing with 2 inch pipe,and while a 1/2 inch more may not sound like a lot ,the difference is amazing!I filled the grey water tank ,opens the valve and it flowed like who goosed the moose, Thanks for all your suggestions

[1Longbow]

Well after spending all day ,under the rv and on top of the rv,I can find no blockage anywhere!
I found that if I tilt the trailer ,with the front jack,the tank drains faster. So my only guess is the design of the grey tank or the angle that its mounted to the under carriage. I'm kinds dumb founded at this point,but I guess it is what it is. Thank you very much for all your ideas,they were all very helpful---Thank you

[Lumpty]

I have a similar issue with my grey tank, but only when I use a Sewer Solution to dump at home slightly uphill into my septic tank inlet clean-out. Regular dump station? Done in seconds. My situation is clearly the outlet restriction of pumping through a 3/4" hose. From the sounds of it, there is something blocking the tank outlet upstream of the blade valve.

[Kit_Carson]

When I bought my Winnebago new in 2008 I had a similar draining problem. After a couple of months and lots of frustration the problem fixed itself.....the disc that had fallen into the tank during construction worked it's way out during dumping. No more draining problems since

[4x4van]

1Longbow wrote:
I thought they must have left a cut out disc in it also,but the tank itself is molded as is the outlet on the tank ,so nothing to cut out.

While the outlet may be molded, the inlet (where the sinks drain into the tank) may not be. So there could still be a cutout disc in the tank.

[mobeewan]

If the tank vent is clear, sounds like something is blocking the pipe between the tank and the 1-1/2 inch dump valve. You may need to pull the valve and see if something is blocking flow against the valve. While the valve is out check the pipe on both sides for blockage just in case.

[downtheroad]

Please post back and let us know what you found and or how you resolved the problem....I like to learn.

[1Longbow]

Thanks for all the answers so far. When draining the grey tank, it comes out at a VERY slow rate. We have a clear elbow,so we can see the the rate of flow. We are not trying to get the last drop out of it,its slow from the start. I thought they must have left a cut out disc in it also,but the tank itself is molded as is the outlet on the tank ,so nothing to cut out. Its raining here today so I'll wait until tomorrow to keep looking. So far the drain pipe from the end where the drain hose connects is wide open as is the slide valve. I'll next try to run water down the roof vent and see what happens as long as everything is apart. Again Thanks for all the help on this

[myredracer]

time2roll wrote:
Rent a camera to go up the pipe.

Or buy a pipe inspection camera off ebay for under $20.

Is this a single grey tank that serves kitchen sink and bathroom? Normally air gets draw into the tank through the roof as the tank is drained. If the roof vent pipe is blocked, I would think the water in the P-traps would get sucked out? You could disconnect one or more P-traps to let air into the tank as it drains and see if anything changes. Could also add some water to the tank and pour some food coloring down the vent and see if it shows up in the tank when you drain it. I think just because you can't feel a disc cutout doesn't mean it isn't there and getting pushed back with your hand. What if it's a sewer rat in there?? :E

You could try some Liquid Drano (our KZ owner's manual says to use it), add some water and go for a drive to let the tank slosh around. It's safe on metal and plastic. We've used it a few times and gets a tank back to factory fresh & clean condition.

[wa8yxm]

Well areas varies as the square of the diamater so a 2" pipe to a 3" pipe (1.5 times the diamater) will have 2.25 times the area and likely about 3-4x the flow.

BUT.... Your problem is something else.. Unless you have like a 500 gallon gray tank it should drain in 2 minutes or less (or if you are using a macerator pump).

If you are using a macerator (Assumption is you are not) you have slow emptying.

Is it possible you have a clogged vent line (Air vent to roof) (I doubt that because the air admittance valves in the RV under the sinks would admit air and let it drain fast) .. I'd say you do have a blockage.

True story:
One RVer, had that problem with his BLACK tank... Turns out when the builders cut the hole in the floor for the toilet pipe. instead of removing the wood to a trash can or recycle can they simply dropped it in the tank.

he double bagged it and returned it to the company CEO.

[Charlie_D_]

A 3" drain line would not be an improvement UNLESS you have a full flow the entire 35 minutes which is not possible with a 40 gallon tank. Do you have a clear adapter at the end of the drain pipe to see what and how much is coming out.

[korbe]

The 1 1/2" drain pipe should work just fine. A larger pipe won't solve a thing. I would first try draining it with more slope on the rig. That could tell if the tank and drain line are not sloped well enough to drain.

[DrewE]

Is it forty minutes to drain, or something like five minutes to drain and thirty five minutes to stop trickling/dripping? If it's the latter, I'd suggest maybe you're just trying to get it too nearly dry.

Angling towards the tank drain should help. Having the output end of the hose as low as possible relative to the RV should also help, increasing the siphoning/suction, though often there isn't much choice in that matter.

[Old-Biscuit]

GO up on roof...remove grey tank vent cap.... IS vent line roughly at roof line or has vent line dropped down into tank which then doesn't vent due to end of vent line being under water.

IF vent line is even with roof line then push garden hose with a pressure nozzle on it down the vent line as far as you can.
Turn on water supply and slowly pull hose back up vent line....have someone watch drain line/flow out of tank

Tanks slow to drain are due to venting issues especially when one has removed drain line and stuck hand/arm in tank.