We install vacuum breaks, airgap, autovent on most Laundry-to-Landscape systems. Fortunately this is a part that rarely fails and is easy to fix. Unfortunately, if it does fail, it is often very inconvenient. Since it is located near the washing machine often, having water spill in this location can be a problem.
Art Ludwig from Oasis Design breaks down what the purpose of this vent is here:
Here are two examples of what we typically install with the picture on the right being most common recently. Both are readily available at Home Depot.
I have had one of each of these, above, fail in the last 8 years (out of more than 200 systems installed by H2OME or overseen by H2OME through a workshop or DIY guidance). The picture on the left shows a 1/2" spring check valve. We use half inch to save on cost, there's no need to have a larger airgap than this. One of these failed within the first year of installation. We installed dozens more of these with no failures reported. To replace this piece, simply cut the 1/2" line directly under the check valve and glue a new one on the remaining 1/2" stub, with the flow arrow pointing down to allow air in, but not water out.
We have transitioned to installing the studor vent on the right in all cases. Mainly, it is less bulky PVC (less costly as well) and replacement is a simple matter of unscrewing the fitting, retaping the threads and screwing in the new fitting. I recently have seen my first failure on one of these, after about 3 years of use. Fortunately it was installed outside, so the water spilled outside. Once I inspected the part, I found that the diaphragm inside had fallen out. It may have been easy to put it back together, but now that it failed, I don't trust it to operate with integrity.