3) Direct the outlet pipe sideways (not angled down) to a Tee. The Tee is vertical. This is where the outlet goes downwards. The vertical pipe (top end of the Tee) goes up though the roof as the vent line.

Hope this answers your first question, "... best way to vent..."

"The Tee is vertical. This is where the outlet goes downwards."

Use the correct type of T.

From the instructions that came with the wall carrier the outlet pipe can not go horizantol. It is either staight down or +- 45 degrees from straight down. So do I ignore those instructions and vent the way Davidro1 said?

Have you called the Grohe technical support number?

The "+- 45 degrees from straight down" is the preferable of the two you wrote in your first post. To answer your question "... best way to vent..."

Your Q "... best way to vent..." is one question. But, you don't need venting as early in the line as I wrote it, or as you wrote it, since toilets are designed to work without being vented. Also.

Post a link to the web PDF that has the Grohe carrier. Then, further discussion can happen in this thread.

I have a Geberit carrier and the pipe can be swiveled sideways.

Lazypup gave the correct answer.

Venting for water closets is determined by your local plumbing code.

Thank you for the replies.

I am under the UPC so I will have to vent it.

I read the manual again and I could have sworn it said it could only go 45 degrees from straight down but I don't see it now. It only mentions the drain pipe going straight down. The manual isn't all that great though.

I am overly concerned about the venting because the last owner did a lot of plumbing work with no permit and apparently no vents. So I am having to redo a lot more than I wanted so it will be correct and work.

Here is a link that might be useful: Grohe manual

The 45 deg angle is a critical angle because in plumbing any line that runs horizontal or rises at an angle up to 45deg above horizontal is technically defined as a "Horizontal Line"

Any line which rises at any angle from 45deg above horizontal to straight up at 90deg above horizontal is technically defined as a "Vertical Line".

In essence what your instructions are saying is that the unit MUST BE attached to a Vertical Line.

Obviously that vertical line from your wall mount fixture will drop down and connect to a horizontal line at some point below the fixture.

Per code the line is a 3" line and under the UPC a 3" line may run a maximum of 8' horizontal from the trap weir to the vent opening.

Under the IRC a 3" horizontal line may run a maximum of 12' from the trap weir to the vent opening, however, there is an exception in the IRC that says if a water closet is the only fixture being served by the 3" horizontal line it may run an indefinite length.

To understand the reasoning here we must consider the reason why they have established maximum lengths from trap weir to vent openings.

For most fixtures the maximum limit from trap weir to vent is to insure adequate venting of the trap to prevent the trap from being siphoned out, thereby leaving the trap dry.

A water closet is the exception that proves the rule. By its basic design a water closet relies upon the siphon effect to lift the effluent up and over the trapway in the base of WC. This also explains why all water closet fill valves are equipped with a "Trap Primer" line to insure that the trap will be adequately refilled during the flush process.

In actual operation a water closet will have a better flush if the length of the water closet waste arm is maximized to the limits allowed by your local code.