Last weekend I ran a 1/2" gas line (black steel pipe) into my kitchen for the new gas range (we had all electric previously)-it's a pretty simple run. Starting from the kitchen there is a brass appliance shutoff which is connected to an 8" black nipple that goes down into the floor. At the end of that there is a 90 degree elbow connected to an 8' length of black pipe that runs through a joist bay straight out the back of the house. From there it 90s down to a 6" nipple, and then 90's along the wall using a tee with a plug in t the other end (for possible expansion one day) with a 10' length of pipe running along the side of the house to where the two 100lb propane tanks will be installed. All joints were sealed with the yellow teflon tape for gas lines. To test the system I rigged up a simple pressure test device consisting of a 1/2" black tee with a schrader valve (the kind you see on a tire), a ball valve (to seal off the pipe when pressurized), and a 0-30 psi pressure gauge. I closed the appliance shutoff in the house, went outside, connected my pressure tester, and used a hand pump to pressurize the line to 25 psi. I know that gas pressure is only about .5 psi, but schedule 40 black pipe is good to 150 psi, so i figured it wouldn't hurt to test it far beyond the normal working pressure just to be sure. I checked the gauge about 30 minutes later and the pressure had dropped from 25 to 20 psi. I then leak tested all of the joints with test solution. All joints checked out except for the joint between the 8" nipple coming up through the floor and the appliance shutoff-I got a lot of bubbles out of that one. I took it off, cleaned all of the old tape off, rewrapped it, and put it back on. At that point I repressurized the line to only 20 psi this time and retested the joint. No bubbles. I rechecked all other joints and again, no bubbles. I went to bed (11:00 p.m.) and rechecked the gauge this morning (7:00 a.m.-so about 8 hours) and the pressure had dropped to about 9 psi, but again, I had not seen any bubbles the night before when I checked the joints. What gives? Is the teflon no good? Should I be using pipe dope instead? I've seen plenty of shops where they use black pipe to run air lines that are holding 100-125 psi no problem so I can't see why my lines can't hold 20-25 psi?