Add the memcached service under the services section in .docksal/docksal.yml:
  # Memcached
  memcached:
    extends:
      file: ${HOME}/.docksal/stacks/services.yml
      service: memcached
Use memcached:11211 as the memcached endpoint.
Complete memcached service definition can be found in $HOME/.docksal/stacks/services.yml.
By default, memcached will be started with 128MB memory allocation.
This can be overridden via the command arguments in the service definition.
  # Memcached
  memcached:
    ...
    # Set memcached memory limit to 128 MB by default
    command: ["-m", "128"]
    ...
Add and adjust as necessary in docksal.yml. Apply new configuration with fin project start (fin p start).