Install a weldless fitting

The weldless sets come with 2 - 1/2" NPT o-rings.  The 2nd o-ring is a spare.

Before you start, dissasemble and clean the fittings with warm water and a mild cleaner like baking soda, Powdered Brewer Wash, or unscented oxygen based cleaner..
 

The hole for 1/2" NPT fittings is just a little bigger than 13/16"   A 7/8" Step bit will have the necessary 13/16" stepping on it.  If you don't have that you can use a 7/8" Hole saw.  The hole will be just a little loose.  Be very careful when using a hole saw as it tends to travel and will make a bigger hole than 7/8.  If the bit wanders and cuts a bigger hole, the fitting will be too loose and will be more likely to leak.  Another method is to use a 3/4" or a 13/16" hole saw and then widen the hole with a grinding attachment on a dremel or a drill.  This will take alot more care as its will be hard to grind the hole round.

Recommended Tools :  1/8” metal cutting drill bit, a step bit or hole saw that goes to 13/16", Metal cutting lubricant, center punch, and emery cloth or fine grit sand paper. An electric or other power drill that will fit the step bit. 

Use a helper if you have one. If drilling for 3/8” fittings you will need a 5/8” drill bit.

Position locknut or shim washer just above the curve of pot or weld on the bottom skirt of keg, mark the center with a permanent marker and use your center punch so the drill bit won't wander. Have your helper hold the kettle or keg and drill the starter hole with the 1/8” metal drill bit. Use slow rpm's (100) and lots of pressure. Use lots of lubricant or stainless steel will case harden and ruin the bits. Clean all chips and burrs from inside and outside the hole. Use sandpaper or deburring tool (dremel) to smooth any scratches or sharp edges on the hole.   Aluminum will cut very easy compared to stainless steel.

Wrap 5 or 6 wraps of white teflon tape on each side nipple threads. Yellow gas teflon tape is thicker 3 to 4 wraps is enough. Wrap in direction of the thread.

Add an oring, and thread locknut on one end. For valve fitting add the coupling after the locknut. Place through wall of keg from inside.
The 2nd o-ring is a spare.  You should not use it on the outside of the kettle.  It will be more prone to leaking.

Site glass: Add washer(s) Add the elbow or Tee and hand tighten.
Weldless fitting: Add the washer(s) Screw on the valve and hand tighten.
Grip the locknut with locking pliers and use locking or adjustable pliers on the elbow to further tighten down the fitting set. Do not overtighten. You just want it snug against the metal. If you have to tighten it all the way down just make sure the o-ring does not pop out.

Site glass: Wrap several wraps of teflon tape on the large thread of the Compression fitting with sight glass and thread into the 90 or Tee. Remove nut from the compression fitting and slide it on the tube. Add the two small o-rings and insert tube end in the brass fitting and hand tighten the nut. The orings will form the seal. Do not put teflon tape on the small thread on the compression side.

Close any valves on the pot and fill enough water to submerge the coupler/locknut inside and watch outside for leaks.
Site glass: Locate the eyehook at the top, drill hole and use nuts to support the polycarbonate tubing. If in a kettle and you will fill above the nut you will need some teflon tape / small o-rings to seal the hole or it will weep.

For a slow drip, slightly tighten the fitting until drip stops. If drip gets worse check the o-ring for proper ensure it is not popping out the sides of washer or locknut.