If your fixture arm (drain line from the trap to a branch or stack) does not exceed the maximum allowable length for a fixture arm and if it is connecting to a vented branch or stack you will not be required to install a vent.

The UPC permits a 2" fixture arm to run 5'.
The IRC allows a 2" fixture arm to run 8'.

If you are required a vent you may connect it in the manner you suggest providing;
1. the point where you install the wye is a minimum of 4"
downstream from the trap
2. The horizontal offset rises at not less than 45deg.

FYI-in plumbing any line which runs from flat horizontal to 45deg above horizontal is classified as a "horizontal line". Any line which is greater than 45deg to straight vertical is classified as a vertical line.

I found this thread which is very similar to my problem. I am installing a toilet, and I have a horizontal 20 foot 4" PVC pipe run parallel with my floor joist across my entire basement. The toilet is the only fixture served by this pipe.

The nearest wall I can vent at is right behind the toilet.

I already reduced the 4" to 3 ", about 6'from the toilet.

I would like to roll a 3x2 wye, run a horizontal 2" pipe to the wall with my vent pipe and up and out.

The thing is, I know a horizontal line is not okay below the trap weir(?) or something like this. I have just recently read this online, after the glue is dried. But, all the self help books show exactly this configuration, or some variation of it, for a toilet vent.

Can someone please help me...

Quote:"I know a horizontal line is not okay below the trap weir(?) or something like this."

That is not correct. What the code actually says is that we may not have any horizontal vents until the vent reaches an elevation at least 6" higher than the "flood level rim" of the highest fixture served by that vent.

From your description the watercloset (toilet) is the only fixture served by the drain line, therefore the flood level rim would be the top edge of the watercloset bowl, which means that you may not have any horizontal run of the vent line until the vent line reaches an elevation at least 6" higher than the top edge of the watercloset bowl.

There are numerous options to resolve your problem, depending upon which code you are under.

Code requires that a watercloset must be installed on the upstream end of a line. If the flush is 3.5gal or greater the line must be a 4" line, while waterclosets with a flush less than 3.5gal should be installed on a 3" line.

We must then consider the maximum allowable length of a fixture arm from trap to vent.

Under the UPC (Uniform Plumbing Code) the maximum allowable for a 3" line is 6' and for a 4" line it is 10'.

Under the IRC (International Residential Code) the maximum allowable length for a 3" line is 12' and for a 4" line it is 16' however, there is an exception in the IRC which states that if a watercloset is the only fixture served by the line it may run an indefinite length. This means that if you are under the IRC and the only fixture served by that line is a watercloset you need not install any additional venting.

Many DIY'ers stuggle under the false notion that they must install a separate vent for each fixture, but such is not the case.

Typically we begin at the lavatory location. We install a sanitary tee on the drain riser for the lavatory, then extend the riser up through the roof as an auxiliary vent. The drain line from the lavatory is then attached to the watercloset line at any convenient point within the prescribed distances stated above. This could be by means of a low heel inlet or side inlet on the closet bend under the watercloset or it could be done by means of a Wye on the watercloset line.

In this configuration the line above the lavatory TEE is defined as a vent, while the line from the lavatory Tee to the watercloset fixture arm is defined as a "Combined Waste & Vent".

The reasoning here is simple. If we install a horizontal dry vent below the flood level rim of a fixture there is a distinct risk that solid particulates in the discharge from the fixture might backflow into the vent line, and in the course of time those particulates will buildup thereby blocking the vent.

In the configuration described above the lavatory line is normally open to permit the transfer of vent air from the roof to the watercloset branch line, however when the lavatory is used the water draining from the lavatory will wash the line below the tee, thus preventing the buildup of solid particulate matter in the horizontal section below the floor.

Thanks lazypup. I guess I'll just cut the vent out that I made on the toilet line. I don't want the inspector to make a deal out of it. I would prefer to leave it and put a cleanout on it or something. There are quite a few DIY books out there that show a rolled wye with 1/8 bend after the closet bend, sending a horizontal section of pipe back at the wall, and up and out for the vent. This is how I installed it. I would rather have the small chance for the vent to be blocked, then no vent at all, even if I may not need it. I copied from the book(s) exactly. I'm on the IRC (ICC?). Really though thank you for your time lazypup, I appreciate it.

You guys really are fantastic for spending your time and giving expert advice. Just wanted to make double sure you know I appreciate the response.

That really painted a clear picture in my mind of "what" is actually happening and "why" it happens.