Well sudo has a short-term memory so once you've entered your password successfully, you have like 5 to 10 mins of grace.
So perhaps some simple command to get the prompt over and done with, then what you really want to do
sudo ls
# now this should work without a prompt
sudo dd if=/dev/sdb | hd | less
Or if the alias is messing it up, try hiding it in a sub-shell
sudo dd if=/dev/sdb | ( hd ) | less
Or just spell it out fully
sudo dd if=/dev/sdb | od -Ax -t x1z | less
