https://imgur.com/a/GONmb1I

I just slightly repaired this and forgot to take a picture, so drew a diagram of what im seeing.

So if you look at the pictures you can see my drainage is all basically in a single line — kitchen sink, dishwasher, shower, bathroom sink, and my toilet connects directly to the cast iron pipe out to septic.

I noticed that when a few of the taps are running simultaneously, It’ll back up and overflow in the open P trap for my washing machine (picture #3).

So I decided to investigate as this is a new issue, and removed the fernco coupling you see in the picture and saw that maybe 40% of that pipe is blocked up. So I got to cleaning it out by pushing a snake into it with a back and forth sawing motion and the jelly just started coming out. That definitely improved the situation but I can’t get to all of it.

So I went upstairs to the furthest drain, and tried running hot water and snaking it, but the problem I’m guessing is that the snake is riding along the sidewall of the pipe and not able to effectively clean the entire 2” width that way. It worked before because I could control the snake head in the immediate area.

Is there such thing as a snake with an expanding head that you typically use in these situations?

Also I have no idea how this jelly even formed. I’m religious about wiping all my grease out of my cookware.