I have never tried it with a bucket, but here are my thoughts.
1. Is the bucket higher than the system being filled? I am not sure you will be able to get the t-line primed well enough to pull water up out of a bucket placed lower than the system.
2. Do you have the loop closed except for the T? I don't think this method will work if the only opening in the loop is the t-line.
I just filled my t-line system by pouring water down the T till it would take no more. Then I cap the T and move the system around to distribute the water in the loop. When there is more room in the T, I add more water. Once the water has moved further into the loop, especially into the pump's intake, you can use the pump to kick the water farther into the system by cycyling it on and off real quick, then add more water.
The bucket would probably be faster if you can get it to work. It takes about an hour to fill and bleed the loop the way I do it.