Hi Lawren,

Water traps in plumbing are to prevent sewer gasses from entering the home. If you’re not connected to a sewer, septic tank, or cesspool there aren’t any sewer gasses to be protecting the home from. The vent is to prevent the water trap from being siphoned as more water flows down. If you have a trap without a vent, the trap may siphon and you won’t have a water barrier to keep gasses from entering the house (the trap will be empty). In your situation there aren’t any gasses to be protecting your home from, so there is no issue with a dry trap or no vent. This is an unusual (to a plumber) situation so they most likely haven’t thought through the reason traps and vents are used and how your home differs.

If you’re not going into a urine tank, but are just flowing urine into the same system, into a greywater mulch basin, then you won’t need a vent either.

The potential drawbacks of not having a vent are 1) the siphoning of trap, which leads to a dry trap which could allow bugs to crawl up the pipe and into your house, and 2) if you have a bathtub full of water and pull the plug to drain it, there may be more gurgling and slowed draining than there would be if it was vented.

As I read your plan I wonder about using just a single mulch basin. If I were you, I’d spread out the flow of water to several basins. This helps prevent slow infiltration or potential pooling at the outflow area, and reduces your maintenance interval.

Hope this helps. And you’d asked about qualifications, which you can read on my bio on this website.

Best wishes,

Laura

Thanks, Laura– for the reply & the speed with which it was produced!  Re. multiple basins, I’m on a slope so have the ability to easily create tiered mulch basins, although in 20 years at my last home I never exceeded the capacity (even living with my 2 children) of my little 3′ diameter basin so I’m not too concerned.  My primary philosophy is “reduce” which makes engineering oh so much easier!