Another Plumbing Puzzler

[larsslc]

I have a 2018 Solitude 310GK-R. I keep having the same plumbing problem. When I set up at a campsite I do not connect the waste line and let some water build up in all of the tanks. After 3 days the grey water tank that serves the shower and bathroom sink shows 1/3 full (about) but the shower stops draining and burping occurs either in the shower drain or the bathroom sink or both. After the burp, it drains fine for another day or so and then the same thing happens again. I can relieve the problem by opening the grey water tank valve and discharging some of the water from that tank. When I do, it is obvious that the tank is pressurized (water comes gushing out thru the waste line for a few seconds and then drains normally. I have talked to Grand Design several times about the problem and they don't know what is causing it. I had the RV in a Grand Design dealer shop for 5 weeks and they didn't fix the problem. Grand Design told them to replace the vent valve under the sink which they did. I told them that wouldn't be a fix because that valve is used to let air into the line and prevent air lock, not to release air into the space under the sink. The dealer said they tested the unit twice and it worked perfectly. Well, I went on a 3500 mile trip and the first time I camped for 3 days the problem reoccurred. We stayed only in RV parks so I could release the pressure when needed, but this winter I am going dry camping for a week and don't want to pull up stakes to go somewhere to dump a half full grey water tank. Grand Design thought the vent line for this tank might be plugged. Three vent lines (2 grey water, 1 black water) go into a common vent line that goes thru the roof. No problem with the other tanks. The particular vent line on the problem grey water tank has a tee about 3 feet above the tank where the shower drain drains thru the vent line into the grey tank. I asked Grand Design about that and they said it was how they do it and not a problem. I just replumbed that shower drain line directly into the drain line from the bathroom sink so the vent line now receives no drain water. Haven't tested that yet. When I was doing the replumbing I also cut into the vent line and checked with a measuring tape that the vent line did not extend too far into the grey tank so that when the tank was partially full the water blocked the vent line. The line extended only 1/2 inch into the top of the grey tank. I also ran the tape up the line for 8 feet and there were no obstructions there. Do any of you plumbing gurus have any idea what may be going on?????

[LCBoyer]

The lower end of the vent pipe is too deep into the tank. JMHO

[howson]

I am by no means a plumbing guru, but I do have a couple of thoughts.

1) Could the sensors be lying? I know the sensors show 1/3 full, but maybe it IS close to full when it starts burping. The capacity of the tank is known, so why not test to see if it will hold the entire amount? According to the specs on Grand Design's site you have a 100 gallon grey water capacity, thus (I assume) that means two 50 gallon tanks. Empty out the problem grey tank and start dumping 5 gallon buckets of water down the drain--will it hold 10 buckets of water? (That may sound like a ridiculous suggestion, but I'd want solid verification the tank can hold its rated capacity without relying on the sensor indicators.)

2) Could there be debris in the tank that floats and blocks the vent as the tank starts to fill? When the tank "burps" the debris moves out of the way for a short period, only to return to block the vent again. (That's about the most SWAG I can come up with.)

3) A work-around is to install a Valterra valve on the dump outlet and open the grey tank valves so the two tanks equalize (behind the Valterra valve). Before dumping the black, close the grey valves. Dump the black as normal and then the greys.

4) The piping arrangement you describe is documented in the manual. Vents & Vent Pipes: Another important part of this system is the vent pipes and vents that release air from the grey and black water holding tanks. The exterior vent cap is attached to the roof and must be kept clear of obstructions to perform as intended. On some models, the vent pipe may be part of the drainage system referred to as a "wet vent" (water flows downward as air flows upward in the same pipe).

5) Not convinced on this one, but you might want to check the vent on the roof. Maybe it is partially blocked?

Please post when you figure it out!

[larsslc]

First I did check how far the vent pipe went into the tank. As I said above, it was only about 1/2 inch into the tank (1 1/2 inch below the top of the rubber grommet on the tank). That was my first thought that the liquid level was coming above the vent line in the tank. As far as the tank being full, it has a capacity of 50 gallons. Before this problem started happening we went to Quartzsite and dry camped for 8 days and this grey water tank was not completely full. I measured the flow of the shower and it is slightly above one gallon per minute - so that's about 50 hours of showers (we don't have a washer which would be connected to this grey tank and there is minimal water from the bathroom sink). Our typical showers are about 5 minutes so in 3 days (and at 3 days is when the problem starts happening) that's 5 showers at most (I only shower ever other day because of a skin condition) or about 25 gallons. When it burps it is good for another 2 showers so the tank is not full. I have checked the vent on the roof and there are no obstructions. I will keep searching for an answer.

[Cate&Rob]

larrssic - This is a puzzling one for sure. For the tank to be "pressurized" as observed when you open the gate valve or when it burps back . . . it has to somehow be sealed from venting this pressure to atmosphere through the vent stack. We encounter a similar situation with our kitchen gray, but I am quite sure this is the vent pipe too far into the tank. It will start to burp back when the vent gets covered and a couple of gallons later it will back up into the sink. We live with this because we seldom dry camp and the fix requires dropping the tank. I have checked our shower gray vent and it is the correct distance into the tank and we do not encounter any problems until the tank is completely full and backs into the shower pan.

The fact that yours was OK and has changed is very puzzling. Could there be something floating around in there that sometimes blocks the vent stack and sometimes does not ?

Rob

[DougW9876]

I am thinking a plugged vent is the best answer for your symptoms. On the roof, pull the vent cap and snake it out or put a water hose to it to be sure it is not plugged.

Is it possible when they cut the hole in the tank to insert the pipe they did not completely remove the piece they cut out, leaving a flap that sometimes covers the vent line? The only way to check that would be to remove the vent line from the tank and look in the hole, or with a flexible camera going in through the dump valve.

It would seem that if there is pressure in the gray tank, there should also be pressure in the other tanks since all of the vent lines are connected together. It really doesn't make sense.

[larsslc]

Update and solution to plumbing problem. The vent pipe was not plugged and the vent line did not extend too far into the grey tank. There is a 45 degree ell on the vent pipe whose lip rests on the top of the rubber grommet in the hole in the grey water tank. The pipe section going down out of the 45 degree ell has a small lip on it that is against the bottom side of the grommet and keeps the vent pipe from being pulled out of the grommet (you have to pull the grommet and pipe out of the tank as a unit). After verifying the above two items (suggestions from replies to this thread), I had replumbed the shower drain into the same drain as the bathroom sink which went directly into the grey water tank and not thru the vent line. I have not tested that solution and it works perfectly. My analysis of what was happening is this. When water was draining from the shower it would trickle down the vent line (which was at a 45 degree angle from vertical) and air would vent out properly. However, if you stepped on the shower drain for a moment, then a slug of water would go down the drain and into the vent line, thus not allowing venting at the same time. This slug would go down the vent line and compress the air in the line and the grey water tank. If the grey water tank was empty, it could easily compress the air enough to drain into the tank. But if the tank was about 1/2 full, there would not be as much air to compress and if slug of water was not big enough it would not have enough head to overcome the pressure in the tank, thus it would remain in the vent line, plugging that line. More water would then drain from the shower, increasing the head of water in the vent line until some of the water in the vent overcame the pressure and drained into the tank, thus further pressurizing the tank. This would continue until the pressure in the tank was great enough to produce a heat in the vent line all the way up to the shower. During this process, you would also get some burps of air overcoming the p trap water head of the bathroom sink. Now with the shower drain not draining into vent line, the vent line is always open to venting and the shower drains fine. I don't know if other RVs are plumbed the same way, but I would suspect this has occurred on other Solitude 310s.

[traveldawg]

Now I need to see how mine is plummed. Thanks for the update, larsslc.