I think I saw this movie in the 90s on Hungarian TV.
It started with a team of astronauts on Venus. There's this thick green liquid and they collect a sample in a thermos bottle. As they do this, a rope snaps and a member of the team falls into a hole. With no way to save them, they decide to return to Earth rather than risks more losses.
They return to Earth and land in a desert. There is nobody to greet them. They walk and walk and walk. Everyone is delirious from thirst and tensions rise. They carry a flare gun and the bottle with the sample. They use a few flares but still nobody comes for them.
They descend into madness and die one by one. The last astronaut shoots and kills the other one with the flare gun. He walks on alone. He finds a well but it's dry. He ends up dramatically drinking the sample from Venus!
Then he arrives in a town? The movie ends.