Any reason why I shouldn't do this...

[domejunky]

I think I've found the world's cheapest sight glass: 15mm tank connector -> 15mm M/F 90° -> JG 3/8 Keg adapter -> 3/8 beer line

Particularly cheap as it uses loads of stuff in my spares box...

Pete

[Belter]

Depends what you're using it for. Beer line isn't designed to go above certain temperatures. No reason why you can use a hose barb and silicone tube though.

[irv]

i have a big wooden spoon that i have made markings on the handle, cheap and seems to work fine

[lord groan]

Go for it!
My sightglass is an acrylic tube, not good to 100c apparently but it was way cheaper than the recommended polycarbonate which is. After fitting to my HLT and running it at a full boil for a while the tube must have got up to no more than 30-40c, so the temp warnings were irrelevant. Having the sight glass in clear air keeps it cool and of course once it's full you really don't get much circulation so the hot water never gets in to the tube.
good luck

[floydmeddler]

I use acrylic pipe too. Very cheap and handles the temps no probs.

[Stanna]

That's basically what I've done if you zoom in on my pic, I used 15mm tank connector to 15mm 90 degree then used 15mm to 10mm reducing connector with 1/2" of copper tube soldered in then pushed my 3/8 acrylic pipe on to the copper pipe it is a real tight fit and hasn't leaked, then I got a piece of 15mm copper pipe cut a long groove in the front and marked off a notch at every liter mark, then just pushed it over the acrylic pipe and there you have it, cheap virtually impossible to brake and takes seconds to dismantle to clean.

[themadhippy]

My ghetto site glass,silicon tube and a few fittings from the spares box

[rpt]

I put a T piece between the tap and pot, stuck a JG adapter in this with beer line. Works well unless the tap is on.