Postgres pg_dump How to make a backup with little space

You can try to tunnel to that machine to that port and restore it or make a backup from any other. From your preferred machine create a tunnel to that other machine where you have the database.

You make this tunnel that passes traffic from port 5432 from the remote machine to the local one, at local port 5432.

$ ssh -N -f -L 5432:127.0.0.1:5432 <usuario_de_maquina_remota>@<ip_remota>  

Once connecting the ports of both machines, you can run on any machine where you did this

$ pg_dump -i -h localhost -p 5432 -U user -b -v -f "/ruta/respaldo.backup" dbname 

And the backup will be saved in any other where you run these commands.
Here the remote machine is the one with your database and the local one is where you want to restore or make a backup.

You can send that backup to another machine and restore it there by running this command on your machine where you have the database and having access by ssh to the machine (clearly with enough memory).

$ pg_dump -C -v -h localhost -p 5432 -U user dbname | bzip | ssh  <usuario_remoto>@>host_remoto> "bunzip2 | psql dbname"

Here the remote machine is where you are going to send the compressed database and then you will restore it in the one-liner and the local one is where you have the database .