Cleanout opening "to the side"?

[Lightningwill]

If I have a waste stack changing from vertical to horizontal, with limited vertical room to incorporate a cleanout, would there be anything wrong with a cleanout fitting on its side (in the horizontal piping immediately after the vertical -> horizontal transition)? Practically speaking, this would be a cleanout tee or wye on its side.

 

[OLD TIMER]

Its ok, make sure you have the wye fitting going the right direction. or you could use a combo with a clean out adapter and plug in place of your sweep, or you could just use a clean-out fitting on the horizontal facing up.