I've been looking for a cheap bulkhead fitting that would work in a mashtun, and I've found one.

I found it at a local hydroponics store (All Seasons Garden Centre, 10027 81 Avenue NW), along with a cheap inline valve. To make the bulkhead fitting work, I'll have to insert a barbed coupler or T into one side of the bulkhead fitting (the guy at the store said to heat up the coupler in hot water, and it would snap in - when cooled it would be locked in and water tight).

Cost breakdown:
5/8" Bulkhead Fitting: $3.75
1/2" Coupler: $1.49
1/2" Barbed T: $1.49
5/8" Valve: $3.95