I wanted to build it myself, but it would have been really difficult to install in this application.
I've heard that happens. I'm too young for it to have happened to me. ;)
Hmmm, even the webpage you gave,
formatting link
gives a picture of an arrester with a piston inside.
I don't think they would do all the things they do -- this is just one method -- to keep the water separated from the air if the air didn't get absorbed by the water.
Hmmm. For the laundry mini-rester, which is a lot like I have, they now want 20 dollars each. I wonder if my retirement account allows for inflation!