This is a thread explaining a simple method of dry testing a loop or reassembled blocks to guarantee watertightness before filling. The current accepted method of filling and crossing your fingers is,to my mind,unacceptable when for $20-£20 outlay you could have a professional leak tester with all the uncertainty taken out. The parts list. 1 1/4" BSPP Equal Tee 1 Pressure gauge,1/4" BSPP thread,20 PSI gauge limit is best as it will allow you to see very small pressure drops easily 1 Schrader valve,1/4" BSPP thread. Assemble like so.... Use PTFE tape on all threads to make a good air seal. Test the unit with a blanking plug fitted,pump it up to 25 PSI and leave it,any pressure loss means a leak,it HAS to be airtight before use. I use a Bitspower d plug on the end as I can just screw on side on then push the unit into place rather than screwing the whole thing on. Attach to your fillport or any port thats free. Pump it up with a hand pump to around 10-12 PSI. Any leaks will result in a pressure drop which the gauge will show. To find those pesky leaks,use a qtip with dish soap or childrens bubble liquid around any suspect fittings,any leaks with blow bubbles allowing for a clean,simple fix rather than having to drain the loop and starting again. For opened blocks,seal the other ports with blanking plugs and pump up,any pressure loss is indication of a leak. There,a simple and nigh on fool proof leak test method.