364 rear black tank

carmex · 07-31-2016, 02:44 PM

So during our first camping week I tried out the black flush on the rear black tank. I dumped it first, then hooked up a hose and turned on the water. I came inside to watch the gauge as I filled. After a couple of minutes I noticed air bubbles leaking up through the seal in the toilet.

Now at this point I did something really stupid: I stepped on the toilet pedal. Of course all the pressure that was building up inside the tank exploded upward, sending the water in the bowl spraying all over me and the whole bathroom. Luckily it was just clean water in there, but GAG it was still nasty and of course the air that was released smelled terrible.

Question is, what is going on here? Shouldn't the air pressure be vented through the roof vent? I'm pretty sure it still isn't venting properly, as I can get the toilet to "burp" by running water into the bowl constantly and just opening the valve a little. After a couple minutes of this, the toilet bubbles to let out the building pressure.

Additionally if I just step on the pedal all the way and open it wide, I get a terrible odor each time. The front toilet is nothing like this.

I wanted to make sure I'm not doing something wrong... no valve or something I don't know about that needs to be opened. And assuming not, any tips on figuring out what's blocking the vent and how to get it unblocked?

RVnut · 07-31-2016, 06:06 PM

All I can say is when I hook to the black water flush and start it up I leave the gate open.. I dont even go in to watch gauge cause they never read right anyway

Bayouownbeer · 07-31-2016, 08:54 PM

Yes you should leave the black take valve open to flush. Never don't it any other way.

carmex · 07-31-2016, 09:40 PM

Hm, I was following the RV geeks guide to flushing tanks:

https://www.youtube.com/watch?v=I6sv4d3PsTo

They advocating filling it up with fresh water and dumping it. In any case, I don't see why pressure should be building up. Isn't that what the roof vent is for? I flushed the forward tank using this same procedure and there was no pressure buildup there.

Krazymace · 08-01-2016, 11:50 AM

Quote:

Originally Posted by Bayouownbeer

Yes you should leave the black take valve open to flush. Never don't it any other way.

X2. I leave it on til water runs clear out the sewer hose.

Sent from my iPhone using Forest River Forums

CHICKDOE · 08-01-2016, 12:27 PM

interesting. regardless of the advice to leave the drain open, why is the pressure building? I can't believe that the water is flowing in faster than the vent can release air. this implies the vent is clogged. now I have no experience in this, but from other posts: leaves in vent? bird nest in vent? toilet paper clog in vent? vent not even installed? is there a check valve in the vent? somewhere on other posts I had read that the round pieces of the cutouts sometimes remain in the tank and plug the drain. could one of these be blocking the vent? can you get on a ladder or the roof and snake something down the vent to check to see if it is clogged? other than that i'm at a loss.

Darugs · 08-01-2016, 12:36 PM

x2 on what CHICKDOE said. I have always let the water fill up a bit when I flush the black tank - just seems to clean it better. I would worry about the gases in the black tank building up on a very hot day and giving you a little surprise.

tkarper14 · 08-01-2016, 01:52 PM

Quote:

Originally Posted by carmex

So during our first camping week I tried out the black flush on the rear black tank. I dumped it first, then hooked up a hose and turned on the water. I came inside to watch the gauge as I filled. After a couple of minutes I noticed air bubbles leaking up through the seal in the toilet.

Now at this point I did something really stupid: I stepped on the toilet pedal. Of course all the pressure that was building up inside the tank exploded upward, sending the water in the bowl spraying all over me and the whole bathroom. Luckily it was just clean water in there, but GAG it was still nasty and of course the air that was released smelled terrible.

Question is, what is going on here? Shouldn't the air pressure be vented through the roof vent? I'm pretty sure it still isn't venting properly, as I can get the toilet to "burp" by running water into the bowl constantly and just opening the valve a little. After a couple minutes of this, the toilet bubbles to let out the building pressure.

Additionally if I just step on the pedal all the way and open it wide, I get a terrible odor each time. The front toilet is nothing like this.

I wanted to make sure I'm not doing something wrong... no valve or something I don't know about that needs to be opened. And assuming not, any tips on figuring out what's blocking the vent and how to get it unblocked?

I have been wondering the same thing. I followed other threads discussing the same topic. Unfortunately, the most common response is something along the line of "Oh my, there is a warning sticker on the tank so you can't do that." Well that doesn't really answer the question does it? I would fully expect the the water to continue to fill the tank until it overflowed through the toilet and eventually spraying out the roof vent, not compressing air in the tank like an aerosol can. It is not escaping through the vent as expected. The pressure is so great that any "bird nest" would be shot out like a Potato Gun. And the probablity of "debris" in the tank left over from the installation completely blocking the vent just seems too low to me.

So back to the OP question. WHAT is going on here?

AquaMan · 08-01-2016, 02:08 PM

Could be such a thing as your vent tube is too deep into your tank. Take the vent cap off and measure down to the bottom of the tube, then to the bottom of tank. Should have 9-10" at least.

carmex · 08-01-2016, 02:15 PM

Quote:

Originally Posted by AquaMan

Could be such a thing as your vent tube is too deep into your tank. Take the vent cap off and measure down to the bottom of the tube, then to the bottom of tank. Should have 9-10" at least.

I'm thinking this might be the problem. I don't notice any pressure buildup until the tank is between 1/3 and 2/3 full and then it begins predictably every time. I will try your advice and see if I can figure out how to measure to the bottom of the tube.

Assuming this is the problem, I guess there's no easy fix?

tkarper14 · 08-01-2016, 03:05 PM

AquaMan - This does make sense. I haven't paid attention to how full the tanks are until the pressure builds like carmex has done. I will start doing so.

Carmex - I could not get any useful information out of measuring from the roof vent on my 369DS. I would advise against the effort. On all three of my vents, I hit what I believe is an elbow between 7 and 9 feet. On the vent I believe is for the rear black tank, I forced the tape measure past the elbow and went as far as 22 feet. So now I am thinking I am working across the MH. Once I tried to retract the tape, it got stuck on the elbow. I took what seem like 20 minutes and a lot of cursing to get it unstuck.

I will take AquaMan's theory as gospel because it seems plausible to me. I have no issues with draining, so there is no need to fix what is not broke. At least (in my mind) I have an answer to my mystery.

Thanks AquaMan.

carmex · 08-01-2016, 03:34 PM

Quote:

Originally Posted by tkarper14

AquaMan - This does make sense. I haven't paid attention to how full the tanks are until the pressure builds like carmex has done. I will start doing so.

Carmex - I could not get any useful information out of measuring from the roof vent on my 369DS. I would advise against the effort. On all three of my vents, I hit what I believe is an elbow between 7 and 9 feet. On the vent I believe is for the rear black tank, I forced the tape measure past the elbow and went as far as 22 feet. So now I am thinking I am working across the MH. Once I tried to retract the tape, it got stuck on the elbow. I took what seem like 20 minutes and a lot of cursing to get it unstuck.

I will take AquaMan's theory as gospel because it seems plausible to me. I have no issues with draining, so there is no need to fix what is not broke. At least (in my mind) I have an answer to my mystery.

Thanks AquaMan.

Agreed, no issues dumping for me either, but I do get smell when flushing after reaching the magic threshold in the tank and as Darugs pointed out, I worry about pressure from heat creating a surprise some day.

AquaMan · 08-01-2016, 05:44 PM

Sent from my iPhone using Forest River Forums

frozen · 08-01-2016, 06:06 PM

It's puzzling to me that some RV manufacturers have problems assembling functional vents. The fresh water tank on my 5th wheel can't be completely filled unless I put my mouth over the fill opening and blow to clear water out of the vent tube. This is probably not a valid procedure for the toilet even if one's mouth is big enough.

tkarper14 · 08-01-2016, 06:58 PM

Now that would be a potty mouth.

swamprat26 · 08-03-2016, 09:14 AM

I think I have this issue on my 2015 360xl on rear black tank. Can't find access to where the vent is on the tank.

Sent from my iPhone using Tapatalk

5nomads · 08-03-2016, 11:43 AM

This seems to be an issue with ALL my tanks. I've been wondering why, when I dump my tanks, I get part way through, everything stops, gurgles a bit, then there's a sudden and loud release (like a vapor lock being released) and then everything continues draining.

Thanks for the suggestion on that, it makes perfect sense.

jergeod · 08-04-2016, 07:23 PM

Okay so we found a possible problem but what is the fix if you pull the pipe up from the roof I would suspect you break the seal at the top of the black tank, how would you reseal it if you can't see it?

carmex · 08-04-2016, 07:40 PM

Dunno, good question. We are planning to try to get it fixed under warranty but will probably wait a couple months until it isn't peak season. I'll post back if we get it taken care of and what the fix was. Maybe someone else has some ideas in the meantime though.

swamprat26 · 08-04-2016, 07:59 PM

On my 360 I located what wall the vent is in but they do not have easy access. Will have to wait until I move it and open my bedroom slide to see if I can access from bedroom side. If Not I would have to pull out my bathroom closet.

Sent from my iPhone using Tapatalk

You may also like: