Searching for the Elusive Coolant Leak

psi means nothing, the tool could bleed down from various sources if theres no leak.
Its not 100% leakproof unless its a brand spanken new tool....
can leak from tool to radiator connection, can leak from the tool to hose connection. Can leak from the radiator connection swivel, etc....

Pressure drop really isnt 100% the Bible & you have an issue per say...

 

Also dont forget to look at the radiator tanks....
passenger side heater core area, firewall, etc..
Not criticizing you, just trying to help, make sure you have the blinders off...
No tunnel vision, dont just focus on the wp area...

 

Yesterday evening I cleaned it up the best I could using brake cleaner spray. The morning, I applied 20psi pressure and it was seeping out around the water pump to engine block seal area. I tightened the three bolts in that area. (The lower one seemed to be looser than it should have been)
Pumped it up again and it seems to be holding. Maybe I got lucky. I'll watch it for now.
Thanks everyone for the input.

 

As stated above, I tightened the bolts that hold the water pump to the block. Thus far it seems to be holding. I put the cover back on and will keep an eye on it. Thank you all for your help.
In another ~ 10k miles I'll be replacing the water pump when I replace the timing belt.

 

That pressure tester and adaptor kit sure looks like a Harbour Freight kit... while it is "adequate" it isnt professional, ill bet the tool leaks.