I'd like to thank Flyguy and anyone else who has contributed to this thread. I recently started wading into AG via the BIAB route. However, I'm a tinkerer and can't leave well enough alone so I wanted to move to a three vessel setup. After reading this thread(and about a thousand others) I took the plunge today and cobbled together a 5g mash tun using a Rubbermaid 5g cylindrical cooler.
I left the stock rubber or plastic grommet in the spigot hole and used all 3/8" parts. Everything fit like a glove. On the inside, I used a 5/8" o ring and a s/s washer in front of a T , with a barb on each side, allowing me to create a loop of mesh braid. I'm not sure that this even makes a ton of difference but I did it anyhow. The outside required 3 washers to give the valve handle enough clearance.
I know most of you would go all s/s, but I was able to find everything in lead free brass. Not ideal, I know, but it fit the current budget. Here's the good part, I put the entire MT together for $46. That includes the cooler.
For those of you in WI, I sourced all my parts at Menards. They have the 5g Rubbermaid cooler for $16. They even had the elusive 5/8" stainless washers.
Now, to upgrade my boil kettle...