The first water barrel (A) on my allotment is at the top of a slight
slope and is fed by rain water gathered from the roof of my shed. I
want to put in a second barrel (B) in a direct line (no bends involved)
from the first barrel and down a slight slope. Both are fitted with
taps, but I would always prefer to drain the water from the lower barrel
B as it is a little more accessible. How best to connect these?

I have options to run a connection pipe from the upper barrel (A) to
the lower barrel (B) as follows:

1. Connect from top of barrel A to top of barrel B
2. Connect from top of barrel A to bottom of barrel B
3. Connect from bottom of barrel A to top of barrel B
4. Connect from bottom of barrel A to bottom of barrel B


Which would be the best option?

Thanks for replies in advance.

Ed