We recently remodeled bathroom. Replaced sewer line for tub/shower. Put in new drain/tub/shower etc. I expected the tub to drain with voracity. But it does not. When the washer drains into the washtub in utility room, the water still backs up into the tub. Very disappointed. What causes this? I know the sewer line is good. It was just replaced.

:confused:

Either you have a clogged drain or the pipe falls the wrong way or the piping was installed incorrectly as to flow direction.

How should the piping go as to flow direction?

It should go down hill. The fittings should point toward down hill. 3" and above shall have 1/8" per foot fall minimum and 2" and below shall have 1/4" per foot fall mimimum

Okay that is not how it goes at all. We put the drain back exactly like it was. Only instead of a drum at the bottom of the tub, we used a p trap. We replaced all cast iron in the bathroom with pvc. From the tub goes straight down approx 18" to p trap. then goes straight across approx 8" ( under the floor joist ) then turns up approx 7"-8" then is pitched down at the rate which you quoted to the 2" line in the wall. The floor joists are notched out to create the fall. How do I fix that? The floor joist is in the direct path of the drain line. I'm assuming that's why they went under it in the first place. House was built in the 50's.

Can you reduce the 18" drop?

Possibly by a couple of inches. Otherwise I will run into the bottom of the floor joist.

Can you connect it at a lower elevation in the trunk line?

No, the trunk line is at right before the foundation wall about 12 feet from where the tub is.

Your previous statement was that it travelled 8 inches under the floor joists. Why can you not pull it up to the bottom of the floor joists? What size it the floor joist?

Sorry let me be sure I understand. You mean the main 4'' trunk... yes? The only way to do that would be to run a separate line altogether. Minimal access under crawlspace.

Main trunk or any trunk. Is minimal space the same as 'i can't get in there and do this'? Or is it just uncomfortable?

It has to make the turn to come up on the other side of the joist and then make the turn to go across the floor.
The 18" is from the overflow down into the crawl. From floor level. There are two floors. Main floor and sub floor with 2" space between. Then floor joist under that at about 7" plus the p trap the pvc is 2''. From the top of the 2" pipe to the bottom of the floor joist is approx 3".

Can't get in there at all. Only about 12-18 inch clearance.

There is a drain line at the wall that the drain line ties into . Then picks up lav an continues on.

Is the problem the drop from the tub? Or that it has to come up from that drop? It has always been that way. We always had trouble with the washer backing up. Could the problem be with the line the washer empties into? Or could it be a venting problem?

Sounds like the piping does not fall correctly therefore the drains are not draining.
Try this, get at least 3 estimates [free] from plumbers to see what they would charge to fix it and let them explain the problem. This way you are not spending money and can brainstorm this with a guy on site.