I use 1" bulkhead for the Bottom Drain, at the lowest point of the pond. It
drains into a vegetable filter/settling tank. With current plumbing, it could
only drain about 30% of the pond. I have to use a bucket to drain the rest. I
would have to lower the plumbing to the same level of the bottom drain to be
able to drain the whole pond.

People here have 4" BD, so they have to use much better BD. Standard bulkhead is
too risky.

"The~Doofie~Man©" wrote:

Question about bottom drains.
I assume they are laid under the liner with slope & installed using the
bulkhead method. This is used for large ponds where one doesn't want to
drain-vacuum the pond all the time.