A question about draining a tank,...

Can I just stick one end of a garden hose into a tank and drain them
that way [I have 7 tanks]. I'm asking this question because a while
back I seem to remember someone saying something about metal being toxic
to fish, and there is metal [copper/brass?] at either end of the hose.
In most cases I will already have most of the fish stored in
rubber/plastic buckets that I've purchased just for that purpose, but I
figured that it would be better to first ask you folks. I thank y'all
for any help that you can give on this matter.~Dean.