for cheap bulkhead connections to pot/tun walls the 15mm compression Tank connector in brass is the cheapest option providing a nice wide sealing flange and 1/2" bsp male thread compatible for connecting to.
for a fully SS option ebay some M20 SS washers (10 pack) and a 1/2" bsp hex nipple
and a 1/2" SS locknut http://www.nero.co.uk/Catalogue/150L...OvnhoCherw_wcB
and a few rolls of ptfe tape..
#1 wrap ptfe round the thread of one side of the hex nipple concentrating on the hilt against the hex.
#2 select a ss M20 washer that fits snugly but not fully up the ptfe wrap to the hilt, there are some minor variances in tollerances so check a few washers for best fit.
#3 a sealing washer can be a 1" silicone oring, or a diy cut silicone baking sheet washer or a good wrap of ptfe round the washer..
#4 then brace the washer and hex against the outside of the hole, and place another washer inside the pot before the nut and tighten to seal. the tapered thread may require a thicker wrap of tape or extra washers inside to create the thrust,, no 2 are exactly the same..
these days i tend to use ptfe to wrap my washers for a seal without any silicone but here is a pic of a connections using a baking sheet washers in my brewkettle, Ive used 1/2" elbow fittings instead of lock nuts to secure to minimise deadspace with an internal siphon..
ps sites ive linked to for bits are just what google chucked up when i was looking for ilustrating pics, so not places ive bought from, i used bes.co.uk for a bulk buy of ss 1/2 fittings for my build to minimise pnp costs..