A sight-glass on the HLT will help measure water into the mash and also (hopefully) be a visual reminder for me not to let the element in the HLT run dry. The kits from BrewHardware look quite good, however due to their length postage is not very cost effective, and the similar kits I could find locally are about $60-70. In addition the information about Polycarbonate and it's relation to being food-safe did not fill me with confidence - even though the Polycarbonate sight tubes are very clear and easy to read.
Using the concepts from BrewHardware's kit, the sight 'glass' for the HLT is very simple; a couple of stainless elbows and nipples, a few washers and a lenght of silicon hose, and hose clamps to hold it in place:
Since the silicon tube is not very transparent, I borrowed the little ball-thing from a kitchen kettle and added a couple of small washers that sit on the elbows so that it does not float away or get lost:
I was asked for some more information and pictures of the sight-glass, so here they are.
Completed, with insulation on the HLT:
Nut - washer - flat silicon washer - keg wall - hex nipple - elbow.
The bottom fitting did not need the extra washers so:
Nut (with o-ring groove) - o-ring - keg wall - hex nipple - elbow.
In the first photo (bare keg with no insulation) the elbows could sit closer to the keg-wall so the fitting hex-nipple could be installed on the inside of the keg (from the inside):
Hex nipple - keg wall - flat silicon washer (or o-ring) - elbow.