re[placed waterpump. still leaks. how do i find the leak

I had the same problem with a 2000 Chevy Silverado Z71. I had to replaced the radiator after 180,000 miles and decided not to initially replace the water pump (if it ain't broke don't fix it). What can and did happen in my case is that hard water scale, almost like crushed rock, can be freed up from your cooling system any time you change a cooling system component. My water pump worked fine and had been changea about 3 years earlier. The gears that turn your water pump are kept dry by a rubber seal. If you get any loose debris in your cooling system (that hard water scale in my case) it can deteriorate that seal in your water pump and the pump starts leaks a slow leak from a weep hole in the front of the pump itself, usually located behind the fan blade. It is always a good idea to do a system flush before replacing your water pump. I did not flush mine because I was replacing the radiator and all the hoses. The scale that I dislodged was in the engine. It is also possible to get a water pump, especially a refurbished one, with a bad seal. Its hard to see the water coming out of that weep hole because of its location behind the fan blade. I had to get underneath with a flashlight and still it was hard to find. I hope this helps.

pressure test the system & look with a bright drop light .if it was the water pump & it still leaks from the water pump you either didn't clean the surface or you left something loose. you have to remove the old gasket or it will never seal. if it s not the water pump sounds like a hose or head gasket.

to look around the weep hole and lower areas, i use a small mirror. something like a 3"X4" girl's purse type or dental nickel size. small mirrors plus a flashllight are good to get by tight areas you need to see.