Troubleshooting slow bathtub drain on slab to septic system

[MoseyingAlong]

A while ago there was a long, interesting thread about fixing a drain situation into a septic system. At the time, it was interesting but had no application to my life. Now it actually applies and I'm not having any luck finding it.

Situation: Bathtub in an in-law unit is very slow draining. Sink and kitchen sink seem to drain fine.
The unit was added to the original house about 15 years ago. In-law unit and main house are separated by the garage. Whole house is on a slab and a septic system. No problems with draining in the main house. I'm thinking it has a separate tie-in to the septic system.
The tub drain goes down a few inches and then turns about 90 degrees (before any P trap).
Haven't found any cleanouts for the drains or septic system. (First experience with a septic system.)


Any suggestions for how to troubleshoot or proceed with this?

And/or a link to the other thread?

Thanks much.

[yachi]

I have one of these on our bathtub drain, and I need to clean it at least once a year.  Hair collects on the screw and forms a large snake in the middle of the drain.  I'd first try and rule that out.

[JLee]

I had to pull the stopper/lever assembly off the tub wall and run a snake through that to clear mine (it wouldn't make the 90 degree bend via the drain).

[clarkfan1979]

I would first try to snake the bathtub drain for hair. They sell plastic snakes that are 18 inches long at home depot for like $3.

[HipGnosis]

Run water into the tub and time how long it takes to 'back up'.  That gives you an idea of where the bottle neck is.
I have to use hair dissolving drain cleaner (Hair clog blaster) about once a year in my tub (also on a slab).
Zep Drain Defense enzyme drain cleaner helps some, but not totally.

[nessness]

I would first try to snake the bathtub drain for hair. They sell plastic snakes that are 18 inches long at home depot for like $3.

This! That'll solve like 80% of slow draining issues, IME.

If you suspect you might have calcium carbonate build-up, baking soda and vinegar works surprisingly well. Just pour in a generous amount of baking soda, followed by vinegar, than cover it with a cloth to stop it from all bubbling out and wait several minutes.

[MoseyingAlong]

Thanks all for your suggestions.

Before posting, we had changed the drain basket and tried the hair snake. Those didn't clear the issue.

Since this is the first septic system we've dealt with, we were hesitant to use any chemical solution.

Today I rented a 1/2 inch snake from Home Depot. We got it started about a foot but then it wouldn't go any further. Turns out there was another tub diverter with a large spring on it that had a very large wad of hair and soap sum wrapped up in it. Don't know why the hair snake didn't catch on it. Anyway, we pulled that whole mess out, cleaned it up and it's draining again. And we're not reinstalling that tub diverter.

So another DIY success!

And I learned for the future that I'll start with a smaller (1/4 inch) snake.

Thanks again.
What a great community.