So, after fixing a section of my vent stack section I got fascinated with the whole design of newer code systems, and then that led me to more reading. I found some articles that suggest concrete septic tank deterioration is caused by H2S gas, and poor venting through to the vent stack can be a significant contributor to this problem. Is that true? I noticed my tank, which is only 20+ years old and it looks like it is starting to deteriorate. I also noticed in my basement there is a slight sag in my main line to the tank; thanks to a previous plumber. I have no issues with flushing, no gurgling sounds, etc, and I have intended to fix this sag for no other reason other than it should be done right. Maybe this sag and the effluent its holding is reducing the venting capacity of this pipe. I realize a bad concrete mix can also be an issue but this has got me wondering.

I'm wondering if it's safe to hook up a garden hose (would be used for cleaning a deck) to a washer hookup. Ultimately if it is, I'd like to split the hookup so I don't have to disconnect the washer to use it.