How to connect a drain to a vent stack?

I would like to install a water softener in my garage. The pipes in the house are set up for hard (cold) and soft (warm) water. However, when they built the house, they forgot to put a drain anywhere near the water softener. The drain is needed to dispose of the brine after regenerating the resin in the softener.
OTOH, there is a 3" ASB vent stack/drain in the wall right behind the water softener. It has a threaded 3" cleanout plug about 3 feet from the floor. The clean-out is in the vertical section.
Originally, they just drilled a 1/2" hole at an angle in the clean-out plug and fed the 3/8" copper pipe for the brine though the hole into the vent. Somehow that does not look like being code compliant, with sewer gases and all.
Is there any legit way I can replace the cleanout plug with a j-trap into which I can then feed the 3/8" brine tube??
It would probably be some kind of Rube Goldberg construction. Just how would I convert the plug to a j-trap? What kind of parts?
Thanks a lot!
--
Walter
www.rationality.net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Walter R. wrote:

Leaving aside a number of Code issues, one could screw in a 3" male adapter where the CO is now. Run that up to a 3" TEE-WYE fitting. Put a new CO in the top of the WYE. Reduce the side inlet of the WYE to accept a 2" P trap (ABS).
It may be necessary to install a mechanical vent (Studor/Oatey) on the downstream side of the P trap to prevent siphonage if the stack carries large flows (toilet flushing).
I would not connect the 3/8" copper line directly into the trap; instead, physically clamp the copper somehow so that it is positioned maybe 2" above the trap inlet. That will provide an air gap that will prevent waste from the stack getting into the brine.
Legit? Nah. Rube Goldberg? You bet.
LOL
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks, but why would your suggestion not comply with code??
--
Walter
www.rationality.net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Good point about the 'air gap'. The rest of the set up is jsut standard plumbing fittings once the screw-in adapter is in place, just keep necking down to get to a reasonable size.
One can do amazing things with pieces from the local plumbers parts bins. I once even built a barrel pump out of standard fittings. Another was a reel for a 1/4" hose line used to water house plants. The rotating axle feed was from one of those 'snap-on' hose connectors.
Harry K
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.