If the air from the drain or toilet smells like sewage this can also be a sign that the vent pipe is blocked.
Slow drain roof vent.
But one of those issues pertains to a clogged plumbing vent.
A single slow drain usually indicates a blockage in the drain itself.
The drain in the toilet bowl is basically a p trap.
And slow drains can certainly be an indication that there s something clogging your main sewer pipe.
However if every drain in your house is slow it s possible this is being caused by blocked vent pipes.
When tubs and sinks drain slowly it may be an indication of an undersized or blocked vent.
Your vent pipe can become clogged from a variety of things.
The odor of sewage.
Elevated drainpipe pressure prevents water from draining off at an average rate.
When the vent pipe is clogged it shows up within your home in a variety of ways from ghost flushing from your toilet to a sink that won t drain properly.
Slow draining is one of the first signs of vent blockages but it s also caused by obstructions in the drain so you need to keep investigating to narrow the problem to a vent issue.
There could also be a clog in the pipe that services the water flow.
The vent system those plumbing pipes that stick out of your roof may be clogged instead.
Slow drains can stem from several issues.
A vacuum is being created that is pulling things in the wrong direction.
Slow clearing drains if the drain just isn t clearing and you ve done everything reasonable to clear a possible clog in the drain your problem may be an obstructed vent pipe.
If the plumbing air vent or vent stack becomes completely blocked a vacuum will form and you will no longer hear gurgling.
If the water moves slowly from bathtub drains or bathroom sinks the problem could be related to improper or inadequate venting.
Without air to equalize the pressure the free flow of water through the drain system can be inhibited.
If you can t clear a slow flowing drain with a plunger auger or drain cleaner the vent blockage may be severe.
If the drain lines in your home have poor venting as in figure a for example water rushing down the drains will pull water from nearby p traps.
Slow drainage slow drainage is probably the most common sign of poorly vented drain lines.
You will also be able to smell sewer gases in the rooms where the affected fixtures are located.
If you notice that one or all of your drains are backed up and very sluggish it could indicate a vent issue.
If the vent line is obstructed it can cause a number of problems including.