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Old 07-03-2016, 01:02 PM   #1
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Join Date: Jan 2010
Posts: 5
SUN #990
1998 Saturn T1700 Plumbing Question?

Hey there all. First post I've ever started. Hello!

Question on sink drain plumbing in the T-1700: Kitchen sink has been backing up lately. Slow/no drain. Bath tub drains without issue, bathroom vanity sink as well...

Thought the air admittance vent under the sink might need replacing. Did that, at a whopping cost of $3 plus tax. When the upright which attaches the vent was unscrewed, the sink drained with a whoosh! FYI: This vent/upright is on the downstream side of the P-trap.

Since replacing the vent ($3 plus tax) and re-installing to its upright, we're back to slow/no drain from the sink. Took the upright/vent back off, and again - sink drained immediately. Unfortunately, the water also came up and out the open upright into the cabinet under the sink... Dang it!

Ahem. Sorry about that.

So: Ran a snake down the upright, getting a little way down the line, but not too far. I think too many bends?

Anyway: Now I'm just confused. Do we have a clog between the sink and grey tank? Can't imagine any other cause... BUT: How could removing the vent (and its upright) allow the rapid drain if there's a clog? Did it end up in the cabinet and I just thought it drained out? Q

'The ultimate measure of a man is not where he stands in moments of comfort, but where he stands at times of challenge and controversy.'
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Old 07-04-2016, 08:13 AM   #2
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Location: Ohio
Posts: 11,150
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H'mm, OK a few questions as it seems you have dug into this pretty good already.

OK you changed out the air vent and it seems to drain out with "woosh" once air can get into the line.

By chance, can you post of pic of the sink trap piping and the air vent?

By chance, did you snake out the sink trap? Is it clear?

Does the drain go slow with the gray tank is empty or when it is more full?

Have you checked the gray tank vent line that goes up to the roof, at the roof line? Some times spiders make a web over the top of the vent pipe and restrict it. You may have to remove the vent cover to tell. And if you do, see if the vent pipe at the roof line seems to have dropped down an inch or more?

A "thought" is the gray tank itself itself is not venting. If it is sealed tight and no tank vent, then it is harder for water to enter a closed tank. The air admittance valve at the sink needs a slight vacuum to open it. if the water is draining so slow because the tank is not vented, it may not create enough vacuum to open the air admittance valve.

Some times the tank vent pipe will slide down into the tank. Pending how far, a 1/2 or 3/4 full or something less then full, the water will seal off the tank vent pipe hanging low and then you have no vent. Or a spider nested over the pipe, usually at the roof line.

What year and model do you have?

Hope this helps


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Prior Sunlines: 2004 T2499 - Fern Blue
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Old 07-04-2016, 06:38 PM   #3
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Join Date: Apr 2011
Location: Maine
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SUN #2097
mainah is an unknown quantity at this point
The vent thing is to allow the gray tank to drain with out pulling the water out of the traps. Both drains in the kitchen sink go to a single drain there is nothing else connected to them. They also have only one trap I would remove the trap and see what might be in it, it is at the rear of both sink drains and goes directly to the gray tank.
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