Hot tapping is also known as wet tapping. It is a way to tap into a water line while it is under pressure and add a line, drain the system or add a Thermowell or sensor. You place a hot tap service saddle or sleeve onto the line. You add a valve and test the connection under pressure with a hydrostatic pump. Then you place the hot tap machine onto the value through a water tight packing gland, open the valve and lower the cutter and retention pilot down until it touches the pipe. You then drill into the pipe manually or with an electric or air driven unit that cuts a hole in the pipe. The retention pipe grabs the cut out coupon so it doesn’t fall down into the pipe where it could cause a problem down he line. You then retract the cutter and pilot up into the hot tap machine, close the valve and you have completed a hot tap.