I purchased my home 4 years ago and was aware of a prior issue with the existing plumbing vent. The issue is, the previous owner remodeled the bathroom and never tied anything into the existing plumbing vent. I have 1 bathroom with a shower, sink and toilet that are not attached to ANY plumbing vents.

I can see the existing plumbing vent from my basment ceiling. It is made of copper and goes to the roof. Every time it would rain, the vent would obviously drip into the basement

For the past 4 years I've been too lazy to do anything about it. I have no idea why the previous owner didn't tap into the plumbing vent as the new PVC piping he put in for the sink goes right underneath the existing plumbing vent!!

So, seeing the PVC piping for the sink is right underneath the copper plumbing vent, I went to Lowes and bought a "Y" shaped fernco coupling. My plan was to go to the basement and cut the PVC drainage pipe for the bathroom sink and connect the coupling to each side of the PVC pipe and the plumbing vent.

After struggling with connecting everything, I finally got it all together. However I have an issue. The issue is, I now have a sewer smell coming from my bathroom sink. It was not there before when nothing was hooked up to the vent...but is noticable now that I have hooked into the vent.

I assume this is not normal?

I realize by me hooking into the plumbing vent from the sink drainage pipe isn't properly venting my fixtures but I figured its better than nothing. After several hours the smell got pretty bad, I unhooked the connection to the vent and put some duct tape over the opening and the smell from my bathroom sink has gone away.

There is a trap under the sink as well. Any idea why my bathroom sink started to smell like a sewer when I cut the drainage pipe and hooked the vent pipe up?

Here is a pic. You can see where I cut the orignal sink drainage pipe and hooked it onto the plumbing vent in the ceiling...

Does anyone roam this forum?

How do you know that the sink, toilet and shower was not vented? Was the sink making a funny noise?
Vent pipes do not run down they need to run up hill. Water down, air up. What may be happening is the drain that you connected to is pulling the water out of the trap under the sink which then allows the smells to rise up into the room.
You need to disconnect what you did and put it back the way it was until you can figure out a way to run the vent pipe up and then into the vent stack. Assuming it was not already done but you did not see it within the wall.

Nothing was making a funny noise. I assumed none of the fixtures were vented because I only have 1 vent pipe on my roof (the copper one in the pic above) and nothing is tapped into it.

It was cut and when it rains, my basement floor gets wet from the pipe dripping. I can see all the plumbing from my bathroom in my basement (minus whats in the walls) and nothing is attached to a pipe that leads to the roof

...

First, please reduce the size of your picture, so we tdon't have to scroll left and right to read the messages.

We can't see what else may be connected to the drain in the picture, either upstream or downstream, but HCC probably nailed it: something is siphoning the water out of your sink trap, which allows the sewer odors to emanate from it.

How do you know that nothing is connected to the vent which runs through the roof? If all the plumbing fixtures worked well, and there never was a gurgling noise from them when they drained, then most likely they were all vented. The connections would be within the walls immediately behind the fixtures, where they would not be visible.

What would your photo have looked like before you messed with the piping? That PVC pipe which you say comes from the sink is way too big for a sink drain, so there must be other fixtures connected to it. If a toilet, particularly, is one of them, it's very possible it siphons your sink trap every time it flushes, thus the odors.

Thank you, Richard. I've hesitated replying here because the problem made no sense to me unless there is a crack in the top of a pipe that allowed gases to escape once the system was ventilated, but having the vent forward (downstream) of both the sink and toilet could do exactly what you describe, siphon the trap dry on each flush.

Ideally, there should be a vent behind each fixture, joined to a main vent somewhere, eventually. In other words, air needs a way to get in behind the water as it drains.

I was racking my brain trying to figure out how a vented system could perform worse than an unvented one and I think you've hit the nail on the head there, Mr. Hetzel. Thank you. (I intended no pun whatsoever referencing a toilet issue by using the term 'head,' by the way.)