Hi all, I am thinking about adding a sink and shower to a corner of my basement that has an existing toilet. The house was built in 1950 and I don't think that toilet was ever vented. Question: if I add a shower and sink, could I vent all three fixtures (toilet, shower and sink) into the Radon mitigation system tube that goes vertically to the roof? If not, is there a simpler way to vent the new shower and sink OTHER than running a dedicated tube vertically to the roof from them? For example, could I run a vent tube horizontally out the side of the house? Any wisdom would be appreciated. Thanks!

We have a 14 year-old house with original basement bathroom with sink, toilet, bathtub. They are in that order of drainage, and connect under the foundation to common drain and backwater valve -Over the 2 years we've had the house, the basement toilet has occasionally clogged (could always clear with plunger) -was infrequently used (by guests), and sometimes I would find the toilet water level very low in the bowl. -Recently (with guests) has been flushing slow and clogging more frequently. -When shower would run, it would suck water level down in toilet bowel and then suck air IN through the toilet. I thought it might be a problem with the vent pipe (if vent pipe blocked, then shower drain is compensating by sucking air through toilet?) -2 weeks ago, had a clog in the toilet. When I plunged it, I could hear gurgling in the shower drain (first time that ever happened). When I turned on the showed, I got bubbles OUT of the toilet (also first time)- so I thought the clog was now in the common drain for the toilet/shower. I closed the bath plug, and sealed off the bath overflow (duct tape) and plunged again. When I was first plunging, I could see the duct tape bowing out (positive pressure in pipes- makes sense with clog). Then, there was big sucking sound (duct tape also sucked in) and the clog cleared. The toilet flushed perfectly. Then, when I turned the shower on, it went back to sucking water the toilet down and taking air IN through toilet (no more bubbling out). My thought was that a problem in the vent pipe was predisposing it to slow flush/clogs. When not clogged, the shower would suck water/air OUT of toilet (poor venting). When clogged, it would push air INTO toilet (clogged drain line filling up with water) We had a plumber come out this week and it was clogged at the time (air bubbling OUT of toilet, when shower is on). He said no way that the problem was the vent pipe (everything else in the house drains fine). I thought it could be the vent pipe connection BETWEEN the basement bathroom and the rest of the house (it takes a 90deg turn above the basement bathroom to connect somewhere in the middle of the house), but he said that was as likely as “being struck by lightning”. He suspected the backwater valve for our basement bathroom, and said he sees the flappers fail/clog in houses ~10 years old. Unfortunately, the BW valve access sleeve through the foundation was not centered over the access plug for the backwater valve, so half of the valve access plug has concrete over it. In short, no way to check it without cutting into the foundation to check and then replace the BW valve. Quote $2000 (cut hole in foundation, check BW valve, replace if faulty, re-concrete with now corrected sleeve). 2nd opinion coming out today. Does this make sense? Fair price? To me, BW valve makes sense for location of current clog, but- before the clog- wouldn’t have this been a venting problem? (air sucking through toilet with shower use) Definitely appreciate any help! :)