Yeah I have a big Snap-on compressor at hand, but a bicycle pump will suffice.
connect a length of tube 4 or 5 foot to one barb and get a car tyre valve, (or bike inner tube valve) in the other end of the tube, you may have to cut the rubber about to get it to fit in the tube.
fit a another tube to other block barb and block it off or crimp it with mole grips etc. now get a bicycle pump and pump up the block if you go too far a tube will blow off anyway just pump until the length of tube is more "solid" to squeeze. now immerse the block in a sink or bath of water and if there is the slightest air leak from the block it will show and let you know exactly where it is.
What I usually do is connect is to about 4 bar, (about 50psi), from my compressors tank and put the block under a an upturned glass container underwater. the upturned container has no air pockets and is see through. Leave it overnight if in the morning there is still no air in the upturned glass bowl then the block has not leaked any air at all and is fully pressure sealed. I'm then happy it wont leak water in my system. overkill?............. maybe but 2 years on...... 8 water-blocks and one splitter in my system..& ZERO leaks
....................... so far
