I have a 16 year old house. On one side, the only fixture is the kitchen sink. On the other is everything else - two bathrooms. The sink drain line goes about 20' across, y's into a 3" pipe that handles everything except one tub. Then the tub y's in a few feet away, and the pipe goes down 3', across the wall and out.

My problem is the kitchen sink and a lavatory sink drain slowly if a lot of water has been used (to clean dishes, shave). No chugging, just slow. If I disturb the kitchen strainer ever so slightly during a slow drain, it seems to relieve a vacuum, and the flow increases greatly. The strainer is not worn or clogged. For short uses, they drain fine. The toilets and shower drain fine also.

Separately, I just had my septic system pumped. I opened the cleanout plug at the exit, and I could see the 10' long pipe going to the septic tank sags at least 3" in the center, evidently from settling. The pipe appeared clean, except some water obviously sitting in the middle.

I just cleaned the kitchen sink trap and pipe going to the wall of scum. Last year I did the same with the lav sink. I went on the roof, and inspected the vent to the kitchen sink. I could see down to the elbow which I believe connects to the horizontal drain line (I assume the sink connects in with a tee above that). I have not yet gotten to the upper roof to inspect the lav vent.

I am a bit perplexed. Could scum like I saw in the trap form over the connection to the vent? Could the sag in the exterior line be related? I am planning to excavate that line and straighten it as weather permits, but I am looking for tips. Thank you!

I'll just address the kitchen. Even a brand new strainer will drain slowly. If you remove it and the water goes down fast enough, no worries.
I throw my strainer (and any sponges) in the dishwasher.
If the 20' is a concern you could install a cleanout in the basement.
Vents usually clog with dead animals, occasionally other debris, not scum. Clogged vents make drains gurgle, I hear.

I appreciate your reply. I am thinking of adding more cleanouts to the run across the house, both the sink and the 3" everything drains into. When the kitchen strainer and the lav stopper are removed, the drains work fine I believe (?? )

I might point out the obvious - the drains worked fine up until recently. Something has changed.

I believe you have a vent issue. It sounds like the drains flow through a 20ft. Pipe before it hits a vent. Your toilet allows air to vent through it when flushing. When water flows through the strainers, it tries to vent through them, as referenced by your comment as to how the flow improves. You are apparently trying to pull water out and it is causing a negative pressure in the piping. If all the drains are clear, make sure the vent lines are clear and you might consider an Air Admittance Valve(AAV) under the sink and lav. This would break the vacuum. I'm not that computer literate but some of the other members -MARK are you there?- can possibly import a picture.

Does this help?

It does Parttime... :)

Thanks... saves me a couple minutes on a busy morning!

Merry Christmas guys!

Mark

Thanks, I was trying to get a placement diagram for donmoore1904.

There is a 1-1/2" vent right at the faucet - I described that I verified it is clear down to the connection, but I didn't rod it. I guess a small bird could possibly block it - pipe is clear all the way down. Each fixture is vented.

https://www.askmehelpdesk.com/plumbing/placement-aav-299252.html

This should help ma0641

I see that now, I was following the 20ft line across to a 3"Wye. Hmmm. I still think it's a vent problem or lifting the strainer would have no effect. Let us know what happens. Brian

Thanks, Brian

Update - I got a 25' 3/8" snake and did the vent pipe - pulled off the trap to the wall, snaked the pipe and came back with some semi-solid scum in auger. Sink worked better. Washed dishes by hand today for 20 minutes, no problem.

Tonight I did a pot of spaghetti. Drained the hot water, and the drain backed up after half the pot went down. The 2" sink drain pipe is 27' from wall to where it tees into 3" pipe from a w-c. The drain emptied after maybe 30 seconds, with no gulping of air or sounds.

After this spaghetti water, the drain now backs up after maybe 10 seconds of faucet flow. I am wondering if the charge of hot water sluffed off scum loosened by the snake and it got stuck downstream. Obviously I need at least 3-5' more length (didn't see this coming when I bought the snake) to complete the 2" pipe. Does this sound like what happened? Thought I had this project done...

Could be. If the water was that hot, you could have a lot of grease in the line and it first melted and then solidified. Any way you could cut the drain line at 20ft. And add a cleanout? If you have space, it's a fairly easy job. You would either solvent cement in a "Y" and a screw in plug or a "y" with a stub and then use Fernco or similar clamps. Solvent cement would be less than $10 in parts.

Solved finally! I realized that adding a cleanout would not preclude me from having to take the sink trap off periodically, so why not try to get a longer snake and go from the sink each time. I also realized that I snaked the main sink first, then the small one (large/small two bowl sink) which tees in downstream a foot, then another foot to the vent connection and down to the 27' run. The new large clog was in the main sink, and backed up with only 1 qt of water. So, off came the main sink trap, and resnaked it.

Either your suggestion I loosened grease that solidified explains it, or I pushed something from the small sink line into the tee. The snake stopped on the small one because it goes in at a right-angle, I assume. Either way this latest clog was near the sink, not 25+ feet away as I assumed.

When I have greasy pans, I always get the bulk out with a paper towel first, but I do eat a lot of beef. I heard that vinegar/baking soda is what a friend uses to maintain her drains - any thought on that? This plumbing maintenance is fun stuff - thanks for listening and helping guys. I can appreciate a methodical approach is in order for these problems. I hit it a bit scattershot.