I can't figure out why my pump will not pump the water from the Franch drain to the street.

Today I did the following:

Took the pump out of the drain. Placed the pump into our pool, plugged in the power, and it pumped the water very forcefully as expected.

I also took my hose, attached one of those rubber stoppers to it, placed it inside the PVC pipe which goes to the street, turned on the water. The rubber inflated, thus stopping up the line which meant the water flowed one-way.. to the street (I went out on saw the clear water coming out). When I turned off the water, the rubber deflated and I did have some water come back into the drain (which tells me I must not have a good grade).

So, the 120 feet of PVC pipe to the street is NOT clogged. I then placed the pump back into the drain, attached it to the pipe going to the street. Plugged in the power. The pump kicks on, but no water comes out at the street. The water level in the drain remains unchanged, even after running for 3-4 minutes.

Any ideas?