I did something similar to bobad, except I used 1/2" pvc and partially filled the one end with mortar by using the pvc like a straw and "sucking" in a couple inches of the mortar(you could probably use a vacuum if you do not want to use your mouth). This went extemely quick. I then partially filled the other end with expanding foam, because I wanted to make sure it stayed upright. I don't think this last step was necessary, though.

-Chris
1 acre pond
Currently managing:
FHM, GSH, GSF, BG, PS, RES, LES, YP, SMB, LMB, HSB, RBT, WE, CC, FHC, and Grass Shrimp