major issue with toilet drain, etc

I've lived in a newer him for about 4 years. Shortly after I moved in, the toilet in our master bathroom starting bubbling and eventually wouldn't flush and overflowed. After plunging, snaking through the toilet to no avail, my uncle cut the pipe in the basement and we pulled out about a truck load of nastiness. No problems since. We installed a clean out where we made the cut, but the clean out is angled down somewhat.

Yesterday I get home and the wife breaks the news that the toilet is plugged in the master bath. So I plunged, used the toilet auger, to no avail. I go downstairs with a bucket and open the clean out (obviously not thinking clearly) . I'm guessing you can imagine what happened next.

My uncle pointed out that the pipe below my toilet, to the sink has virtually no pitch. Then there's a couple of 45's, then the shower ties in. There's one spot at this junction of the shower that the pitch appears to go uphill slightly for a couple of feet, then starts downhill like it should.

What needs to be done here? Any help appreciated, I can provide pictures later.

Thank you

All drain pipe must be installed 1/4 inch per foot slope . Clean outs are best installed in the floor level leading to the city main. You can rent a 1/2 cable with three inch blade at Homedepo pull a toilet a cable thru there

Unfortunately there is no easy fix. Start at the lowest elevation and work your way to the highest elevation by adding 1/4" per foot slope as ExtraMilePlumbing pointed out. You may have to notch things, add spacer,s or even cut out sections of piping. As the old saying goes, sh#+ rolls downhill.

post pictures...maybe...............

Install a ejector pump if you don't have the room maybe?