The relocation of my upstairs bathroom requires the change of the 3" abs drain pipe. The pipe starts at the toilet, after approx. 3 feet of horizontal run a 2" shower drain is connected with a Y-piece. Then after another 2 feet is a 1 1/2" sink drain connected with another Y pice. After 1 foot of horizontal run I want to put a 90 elbow pointing downwards. Right after this I want to put another 90 elbow going to the left side. Then there is a 5 feet horizontal run before it finally connects to the drain stack that disappears in the basement floor. Is this going to work or will I get problems at the two 90 turns? Instead of using the two 90 turns I could also use 45's. But there is still the 5 feet run before it connects to the 3" main stack. Any help woould be appreciated.

I don't see a problem. Won't hurt to use the 45's, but even more important is to make them the longer radius DWV elbows. Likely that is at places like Lowe's or Home Depot stock in 3''. Verify what you have really is ABS and use cement meant for ABS with it. If you have to mix in PVC, get the cement meant for either.

I posted this question also at the "fine homebuilding" forum and the concerns were that after the two 45's the flow what not be enough to transport the solids the remaining 5 fet before it enters the 3" main stack. The sugestions were to install a cleanout on the last 5 feet run.

I am not the top dog in plumbing here. If Speedball says it is OK, do it. I might point out that in some comercial building on a slab, drains run hundreds of feet horizonally just under the floor.

The relocation of my upstairs bathroom requires the change of the 3" abs drain pipe. The pipe starts at the toilet, after approx. 3 feet of horizontal run a 2" shower drain is connected with a Y-piece. Then after another 2 feet is a 1 1/2" sink drain connected with another Y pice. After 1 foot of horizontal run I want to put a 90 elbow pointing downwards. Right after this I want to put another 90 elbow going to the left side. Then there is a 5 feet horizontal run before it finally connects to the drain stack that disappears in the basement floor. Is this going to work or will I get problems at the two 90 turns? Instead of using the two 90 turns I could also use 45's. But there is still the 5 feet run before it connects to the 3" main stack. Any help woould be appreciated.

I posted this question also at the "fine homebuilding" forum and the concerns were that after the two 45's the flow what not be enough to transport the solids the remaining 5 fet before it enters the 3" main stack. The sugestions were to install a cleanout on the last 5 feet run.

I don't like to see "dog legs" in drainage but sometimes they're necessary. Use long sweeps to make the offset. If space is tight short sweeps are acceptable. I'm a great fan of adding cleanouts, but not when they're unnecessary. The sheer volume of water will carry the solids to the stack.
I don't quite understand the reasoning of "Fine Homebuildings" answer. Five foot is a very short run to install a clean out on.
If I were concerned that the layout you provided would clog up and you would have to have a "handy clean out" to keep it operating I would have given you different options. Oh well!
Good luck, Tom

Thanks for your advice Tom.