Question About Flat Wyes

At the risk of asking a question that's been asked a hundred times (wye is too general a term to search on), is connecting a horizontal branch line to the main horizontal drain via a flat wye allowed, a bad idea, or both? I have it in my head that it's allowed but can lead to problems down the road.

Thanks,

Sam

If you are talking about a "T-wye" YES YOU CAN . If it is a Sanitary tee / or short turn tee no you may not .

Short turn/sanitary tee should only be used from the horizontal to the vertical . Long turn or t-wye is allowed for either.

Cal

Thanks Cal. Definately not talking about sani-tees or vent-tees on the horizontal. Speaking of that incorrect fitting usage, the DIY'er that redid the drain lines in the house we recently bought used sani-tees for all horizontal branch connections along with 90s, about half a dozen ferncos, a four inch to three inch transition, no cleanouts, and some of the most creative pipe supports I've ever seen - string, left over fittings, and a tree limb. He was so proud of his work he had the relator point it out to potential buyers as a "plus".

Thanks again,
Sam

When cutting vents into a horizontal line, they must take off between 45 degrees and vertical.

vents

That is the ideal, but not always possible in the "real" world.

Clarification

Just to clarify, I was talking about horizontal branch drains connecting to the main horizontal drain using a flat wye. I had it in my head, from somewhere, that these connections worked best if rolled.

As for vent connections to the horizontal using a wye, if you can't roll it somewhere between vertical and 45, don't you assume that at most a correctly sized pipe will never be more than 1/3 full and work from there?

Thanks,
Sam

vent

As a practical matter it really doesn't matter, because by the time the vent has to function, the water in the pipe will be at a minimum.