Problems clearing drain

The bathtub filled up with effluent when draining the laudry tubs. I am on a septic tank.
At first I figured the tank was full so I had it drained. The guys who did job said it did not look full and that they noticed nothing entering the tank when the toilet was flushed. I opened the cleanout access and used a snake to poke through a not very difficult blockage. The snake goes through easily to it's fullest length, (50 feet).
However when I close the cleanout and switch on the landry tub pump again it quickly backs up into the tub again!
To make sure there was not a blockage behind the cleanout I checked with the drainout cap off that the water from the laudry tubs is coming the right way. It comes through fine to that point but stops very quickly. The water level in the drain pipe then slowly goes down will the pipe is almost empty.
Am I correct to assume there is still a blockage in the drain? How would I go about getting it cleared?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
weeG wrote:

Well it would appear you have a blockage beyond the drainout cap (whatever a drainout cap is?) and it needs to be snaked. Are there any trees along the way?
You may need a longer snake or maybe just call the pro out.

--
Joseph Meehan

Dia duit
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

No trees (drainout cap is a typo...sorry).

I'm using a 50 foot snake. The cleanout is 2 feet from the wall and about a foor or so below grade. The blocks in the wall are 12 inch. The tank is 5 feet from the outside wall. The top of the tank is 1 foot below ground.
I tried going to a plumbing supply house and they sold me a bottle acid. It took a couple of tries but seems to have cleared the blockage.
Thanks for your help and attention. Let's hope the fix is permanent.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.