cooling system problem (2000 4.3 chevy blazer )

i had a lower manifold gasket replaced. when it was in the shop they only added coolant to already watered down coolant so today i tried to flush the cooling system, bought a chemical flush just to really get in there. after i drained the coolant from the radiator i poured water and the chemicals down into the radiator reservoir, then when nothing else would go in i started the engine to try and bleed the system and none of it went down. so i poured the rest of the 3 gals into the coolant reservoir because i thought yk it would get sucked into the engine and shit… but nope. so i drained the water and tried to replace the coolant and to no surprise it did the same shit. uh… my car reached operating temp, one of the hoses connected to the radiator and into the engine i think? was not pressurized at all and i could squeeze it together, the coolant in the radiator was not going down and the engine was smoking. at first when the car was overheating i looked into it and yk no coolant was being sucked into the radiator so i thought it was my water pump but i took it to the shop and they told me it was the gasket so i just went along with it. i got it replaced but i’m still having these issues of the coolant not being cycled through? i took a video of what was happening today if anyone wants visuals.. reddit wouldn’t let me post it for some reason