The following is a guide for a simple to build sight glass. You will need the following: Masking tape Spirit level hacksaw Adjustable grips or spanners 20mm cutter 2 X compression tank connectors (Screwfix part no. 82376 £2.24 ea) 2 X Conex brass pushfit street elbows rl](Screwfix part No. 54152 £2.49 ea) polycarbonate tube 15mm X 11mm (2mm wall thickness) (One stop plastic shop 2m length was £16.21 plus carriage) With a bit of luck you will end up with something like this: First of all place a piece of masking tape in the position you want the sight glass. Then use the level to true up the pot and scribe a vertical line. Decide how far from the top and bottom you want the tank connectors, i think mine were about 35mm (there's no point having a glass that goes out of range) then mark the vertical line to give the positions for the tank connectors. I was cutting through a stainless stock pot so I centre punched and cut out the holes with a 20mm 'Q Max Cutter' Fit the tank connectors using your choice of washer, I used 1/2" poly washers as I had some on the van, these have been my choice of seal as you can really tighten them up without them 'spreading'. Next insert the street elbows into the tank connector but don't tighten it up yet. The elbows have an 'O' seal so there is no risk of damaging the poly tube. Measure the distance between the two elbows, making sure you allow for the tube to go fully home into the elbow. Measure this at least twice as once the tube is cut and inserted into the fitting it is there for ever. Cut the tube to length and debur the ends with a craft knife or file Remove the elbows from the tank connectors and fit the tube. Install the sight glass and elbows back into the tank connectors and tighten up the nuts onto the olives. The glass works really well but I have only tested it with clean water so far. There may be more to come on this as I am experimenting with a Chevreon/ stripe/ chequerred backing for the tube to make the level super obvious even if it discolours in the boiler due to the hops. I took the photos after I had finished the build so apologies for the lack of them .