PHP flush() isn't doing anything

PHP SDK
3

Positive its checked, I have also run this command to be sure.

./couchbase-cli bucket-edit \
	-c 127.0.0.1 \
	-u Administrator -p pass \
	--bucket=default \
	--enable-flush=1

I have 2 servers in the cluster, I am not sure if doing it on one server in the cluster is fine.