4" or 3" Water Closet (Toilet) DW pipe

[Dohc]

Is there any reason I would NOT want to use 4" pipe all the way to the toilet flange. I could reduce it down to 3", but it is just as easy to keep it 4" and uses less fittings (no need for a 3" to 4" reducer). Is 4" ok?

As for the vent, that is about 5' away and will be 3" to fit in the wall.

 

[Terry]

The toilet can be a 3" and the vent can be a 2"
You can also do the whole thing in 4" if you want.

I think 3" has better drain line carry for a single or double installation. Water kind of flattens out on 4".

 

[Sponsor]

 

[Reach4]

If you use 3 inch pipe, you should consider a 4 x 3 closet bend at the toilet. There are various forms. The one pictured is the "spigot" type.

If you have a lavatory as part of the install, that can often serve to vent the toilet too.

 

[Dohc]

I will use 4" all the way to the closet flange then as it is less parts.

Could a lavatory, using a 2" pipe running about 6', drain and direct vent into this 4" between the toilet and 3" vent?

Thanks for all the help

 

[Cacher_Chick]

With the reduced water use fixtures of today, there is no reason to use 4”, except as a building drain. Using 3” allows the pipe to be scoured properly, which reduces clogging.

A toilet can be wet vented through the lavatory vent, by connecting the 2” drain downstream of the closet bend.

 

[Dohc]

If you use 3 inch pipe, you should consider a 4 x 3 closet bend at the toilet. There are various forms. The one pictured is the "spigot" type.

If you have a lavatory as part of the install, that can often serve to vent the toilet too.

Reach4, interesting that you suggested the 4 x 3. After looking closer, I think the code requries a 4" closet flange...

(c) Water closets. A water closet shall discharge through a drain pipe or fitting with a minimum diameter of 3".
2. A floor outlet water closet shall connect to a 4 inch or 4 × 3 inch closet collar fitting. A 4 ×3 inch closet bend fitting may be installed where a 4 inch closet collar fitting is used.

Do they even make a 3" closet flange?

 

[Reach4]

Do they even make a 3" closet flange?

Yes. Lots of them.

Possibly the most common is a "4 in. x 3 in. " Closet Flange. It glues either outside of a 3 inch pipe or inside a 4 inch pipe.

There are 3-inch inside. 3-inch outside. The 3-inch inside are often avoided because they have the narrowest passage, although that passage is still bigger than the output of a toilet. There are all kinds of variations.

A 4 inch pipe or closet bend has the advantage that both the inside and outside can be used over time, which can come in handy during rework/remodel.

Some flanges use compression rather than glue. Those would seem to be an advantage to those who are less practiced and might be concerned about the need to get it right the first time with glue. I am not a plumber.

Stainless steel rings on the closet flange are more sturdy than plastic. They are more rust-resistant than painted steel, although the painted steel should be good for decades.

 

[hj]

Whether you use 3" or 4", the "number" of parts is the same, if it is done properly.