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Old 09-16-2018, 10:33 AM   #1
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Bathroom sink not draining. Isata 5 DS

Anyone out there have a slow drain in the bathroom sink on an Isata 5? The sink drains into the black tank right at the black tank vent stack. When I took delivery there was no slope on the drain line but the factory service center put some slope on it. While there was some improvement after that it still drains slow and the last cup or so of water bubbles up as if the drain doesn't have enough venting going on? The water lever in the 'P' trap is only about half an inch below the sink strainer. Isn't normal that the water level in the 'P' trap would be lower? Anyone else have this problem, can you see water in your 'P' trap up close to the sink? If you solved this what did you do? I'm tempted to cut into the wall and connect a 'T' so that the Bath sink drains into the gray tank. Ideas?
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Old 09-18-2018, 04:34 PM   #2
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Anyone out there have a slow drain in the bathroom sink on an Isata 5? The sink drains into the black tank right at the black tank vent stack. When I took delivery there was no slope on the drain line but the factory service center put some slope on it. While there was some improvement after that it still drains slow and the last cup or so of water bubbles up as if the drain doesn't have enough venting going on? The water lever in the 'P' trap is only about half an inch below the sink strainer. Isn't normal that the water level in the 'P' trap would be lower? Anyone else have this problem, can you see water in your 'P' trap up close to the sink? If you solved this what did you do? I'm tempted to cut into the wall and connect a 'T' so that the Bath sink drains into the gray tank. Ideas?
You and I must have coaches that were built on the same day because we seem to experience the same exact issues!

So yes, our lav sink drains very slowly AND we get the bubbling/gurgling as the last little bit drains out of the sink. The “funny” part about this is that you and I have different floor plans, so our sinks, drains and vent stacks are in completely different places! As of now, I have done very little investigative work, but it’s interesting to hear that you had the factory add extra slope for the drain under the counter. I will have to look into that for sure.

Here's a THEORY: the rain cap that is glued to the top of the vent stack COULD be considered a hindrance all on its own. Think of it like a pipe “cap” that has a bunch of tiny holes in it. If I were to guess, I’d say that from a surface area perspective, it’s 30-40-ish% blocked. I’ll stress, that’s a GUESS, but what I can say for certain is that the vent stack rain cap is _NOT_ flowing enough air to render the 1.5” vent stack as effective as a 1.5” vent stack should be. If we say that my estimate is anywhere near correct and 30% is the number, that would reduce the 1.5” pipe to 1.05”. If it’s 40%, then we would be talking about effectively reducing the pipe to 0.90” instead of 1.5”. Probably not a huge issue for draining the sink, but it’s certainly not ideal for draining the 3.0” drainpipe/valve when you go to dump your blank tank.

The rain cap for the vent stack on our (both of them) look exactly like this one:
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Old 09-18-2018, 04:43 PM   #3
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The rain cap thingy, is actually a 360 Siphon developed specifically for this purpose by a retired engineer. Since its creation, the company was bought by Lippert, but to my knowledge, nothing has changed.

https://www.lci1.com/360-siphon
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Old 09-18-2018, 05:01 PM   #4
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The rain cap thingy, is actually a 360 Siphon developed specifically for this purpose by a retired engineer. Since its creation, the company was bought by Lippert, but to my knowledge, nothing has changed.

https://www.lci1.com/360-siphon
Huh. That is interesting and thanks for posting.

I’m not a aero or fluid dynamists…..dynamissyst…..arghh, I’m not even sure tis that’s an actual word, but I CAN say that when I go to drain the black tank (no matter how full it is), if I just rip open the drain valve, it will easily air lock inside a few seconds. Once or twice now, I’ve had it air lock so badly that it simply stopped draining. Now I’ve just gotten into the habit of only pulling the valve open 50-60% and just accepting that it’s going to take a little longer.

If I look at any actual sticks-and-bricks building code, it will usually say that the vent stack MUST be half the diameter of the drain pipe that it’s venting. So, the black tank drain is 3” and that would suggest that the vent stack should be 1.5”, which it is. However, from a surface area perspective, the cap is certainly cutting into that. Since it sounds like the rain cap/odor siphon thingy was really designed to be effective at drawing odor out when there is no flow in the drain (according to the YouTube video above), I really view it as a hindrance from an airflow “I need to drain the waste pipe” venting perspective.

Again, I’ll stress that this is coming from someone who can barely spell dynamisyst…..dynamisois….dynometer….oh, I give up!
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Old 09-18-2018, 05:03 PM   #5
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.....but I also don't think that is the problem with the sink draining. The sink drain is 1.5", so the vent should only "need" 0.75" to be fully effective.
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Old 09-18-2018, 06:18 PM   #6
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Thanks, I'll try draining the sink w/o the cap installed, see if that makes a difference?
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Old 09-18-2018, 06:31 PM   #7
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Thanks, I'll try draining the sink w/o the cap installed, see if that makes a difference?
I was thinking the same thing when I climbed up there to check it.....actually, I was thinking that I'd climb up there, pull the cap and shine a flashlight down the vent to inspect for blockage. That's when I discovered the cap thingy. Alas, it's glued on and with not a lot of vent stack sticking up to potentially buy another cap and then glue it on.....and based on the video Brian posted above it LOOKS like the cap maybe be flanged and then sealed to the roof, but I'd have to climb back up there and check again.
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Old 09-18-2018, 09:20 PM   #8
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You and I must have coaches that were built on the same day because we seem to experience the same exact issues!



So yes, our lav sink drains very slowly AND we get the bubbling/gurgling as the last little bit drains out of the sink. The “funny” part about this is that you and I have different floor plans, so our sinks, drains and vent stacks are in completely different places! As of now, I have done very little investigative work, but it’s interesting to hear that you had the factory add extra slope for the drain under the counter. I will have to look into that for sure.



Here's a THEORY: the rain cap that is glued to the top of the vent stack COULD be considered a hindrance all on its own. Think of it like a pipe “cap” that has a bunch of tiny holes in it. If I were to guess, I’d say that from a surface area perspective, it’s 30-40-ish% blocked. I’ll stress, that’s a GUESS, but what I can say for certain is that the vent stack rain cap is _NOT_ flowing enough air to render the 1.5” vent stack as effective as a 1.5” vent stack should be. If we say that my estimate is anywhere near correct and 30% is the number, that would reduce the 1.5” pipe to 1.05”. If it’s 40%, then we would be talking about effectively reducing the pipe to 0.90” instead of 1.5”. Probably not a huge issue for draining the sink, but it’s certainly not ideal for draining the 3.0” drainpipe/valve when you go to dump your blank tank.



The rain cap for the vent stack on our (both of them) look exactly like this one:


Make that 3 built on the same day...
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Old 09-19-2018, 05:56 AM   #9
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Make that 3 built on the same day...
Make that 4. Mine does the same thing.
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Old 09-19-2018, 07:12 AM   #10
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Mine as well, and it’s an Isata 3rw.
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