I do the same as mrb604 -- pour your bleach into the water filter housing (take the filter out first) and then fill the tank. If you don't have an external water filter, and you want to go this way, check at a Wal Mart -- they are not that expensive. As a rule, I will once a year santize my water filler hose by putting it after the filter (between the filter and the MH) and then fill the tank letting the mix go through my water hose.
Just some thoughts to consider.
Dave and Karen -- '02 Ultimate Advantage 36 C, 350 HP Cummins, Allison 3060 Tranny
'13 Ford Edge, InvisiBrake