Confused on Drain Line Routing

I am confused on the drains in my crawel sapce. Discovered this after a major blockage stoped up all lines ! Cost me over $200 to get cleared... The plumber then questioned the way the lines were routed.

Note from the picture that all the drains of all the fixtures from the house run into the 4" main line running North to South (Left to Right) , then turn 90 Deg run for about 8 feet ( This is where the blockage was) and Turn again 90 Deg and run without any drains connetced to it some 25 feet Back to the North ( Right to Left) in a 4" main.

Cleanoiuts are only on the 2" lines ( C and CO notations )

Makes no sense to me why the fixtures were not connected directly to the South to North Main directly without the long travel loop.

The House is only 3 years old.

Can anyone help on this ?
Should I cut it all out and run each drain into the South to North (Right to Left) line ?

Thanks for Your Help
Kevin

Without knowing the actual on-site conditions or being able to see the actual venting and reasoning behind that design..all I can say is wow. Doesn't make much sense to me.

dwv

four possibilities.
1. This is a mobile home which was preplumbed at the factory.
2. This is a modular home which was preplumbed at the factory.
3. The installer was told the incorrect location of the sewer termination before he installed it, and thus had to reroute the line to the new location.
4. The installer was incompetent, or only knew how to put plumbing in one way.

Home Type

Thanks - Your Last 2 options are possible as this is a stick built home on a 3 foot crawl space.

3. The installer was told the incorrect location of the sewer termination before he installed it, and thus had to reroute the line to the new location.
Could be possible but the septic tank location must be staked and set prior to building Here in North Carolina.
4. The installer was incompetent, or only knew how to put plumbing in one way.
Seems to be most likely

Dwv

The septic location has to be "staked" or determined before the plumbing is installed ANYWHERE in the world, unless you wish to have a situation such as yours. We are not omniscient when it comes to figuring out WHERE someone is going to put the septic tank, ESPECIALLY since the location could be dependent on circumstances that we do not know about.

I would pick #4. But he may have got turned around for some reason??? There are incompetent contractors out there but much less in the electrical and plumbing fields are they are usually licensed. Could just have been a rookie mechanic working for a contractor.

drain

To answer your original question. To do it correctly, you would have to cut out and discard the entire system and redo it with ONE line from South to North which everything connected into. The existing system would be useless and more expensive to redo because all the connections face the wrong way.