intermittent drain issue

deepstuff

Hi,
I have a two story house on a septic tank. last week while draining the jazuzzi tub on the second floor it made the toilet next to it bubble and would have overflowed the toilet on the second floor if I didn't stop it. I used a plunger (for ten minutes) in the first floor toilet and it immediately drained (to lower than normal level). I was also then able to drain the rest of the tub without issue. Thought I had the issue solved as I used the tub without issue the next time. but several days later the same thing happen while draining the tub. The upstairs toilet and bath feed into a 3 inch line which changes into a 4-inch in the basement. The downstairs toilet is on another 3-inch branch line that is farther downstream than the first by about 10 feet, then there's another 15 feet to where the 4-inch line exists the house.
Wax seal is now leaking on downstairs toilet, I think I blew it out with the plunger.
Do I have something in the 4-inch line that is moving (plugging and unplugging? Is there something happening in my septic tank? Could it be a vent problem?

TKS

joecaption

Drains plugging up someplace, septic tanks full, leach field has failed.
Could be anyone of these.
If a drains not completly plugged up it will still drain just slowly, by trying to dump that much water down the drain at once it's filling up the pipe and has no where to go so it backs up. Leave it a while and all the water drains.

If I was on a septic I would not be dumping that much water down the drain.
I'd be using a pump and just dump it out a window.

deepstuff

O
Don't think its the leach field or septic tank full - had it cleaned out a year ago and once I plungered the toilet all water went down right away fast and worked several days including draining the tub at least once. Could it be a partial blockage that I'm moving with the plunger? Is so what can I do? Could it be a vent blockage?

I can't pump my tub out the window. House is 12 is years old

deepstuff

Water that went down after plungering included what was in toilet and the second half of the tub I had stopped.