Softener Drain - Tie in above existing P Trap?

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Ben Lomond Ca
Hey all,

Been lurking for a while but can't find the answer. Softener is draining outside but it's starting to do some damage to existing plants and so want to bring the line in to our septic system instead.

Problem is that where the softener is located doesn't have a drain of any kind.

It does share a wall with a bathroom, and the p-trap for the tub is easily accessible from the crawl space.

Putting in a standpipe and airgap could work but the space is tight and along the foundation perimeter, and would take some drilling to get a proper sized pipe through the foundation wall and into the crawl space. Since it's tight, there also wouldn't be enough clearance to keep the standpipe in the crawl space, and just run the .5" softener hose to that space.

At .5" the softener drain hose would be an easy fit to slip in to the crawl space next to the main copper line, and the softener itself has a built-in check valve.

So, I was wondering why I couldn't just put a saddle drain before/above the bathtub's trap with a check valve quick connect and just drain into the tub's existing drainage from there? Similar to how RO system drains look.

Trying to avoid a cross connection if this crosses that line but since it would function similarly to a washer's standpipe, would have a P trap, 2 check valves, and isn't on the main sewer line, just looking to understand what to watch out for if anything.

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Hey, wait a minute.

This is awkward, but...

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