How can I access my time capsule through ssh? I am trying to reach the time capsule on a remote network. After following the advice of another question I realised the router/network doesn't support NAT-PMP/UPnP and thus I get to configure the time capsule as available through icloud, but I'm never able to reach it outside of the network.

However, I am able to ssh into an old powerpc I have port mapped on the router to a static IP. Is there any way to tunnel the time capsule backup through ssh? I've also tried sshuttle which works perfectly to forward dns/http requests. But it doesn't seem to make time capsule backups available, since the finder doesn't show any shared devices on the network.

I would gladly try a solution like FreeLan but unfortunately their support goes back to 10.7 and the old PowerPC machine inside the remote network serving as entry only has 10.5.x.
You would need to forward TCP port 548, which is AFP (Apple Filing Protocol). This is the storage protocol used by Time Machine to access content on a Time Capsule.

Note: This will not necessarily make it possible for your remote systems to auto detect the Time Capsule - as any DNS information (Bonjour) you forward would probably be incorrect as it needs to be translated (i.e. a different IP-address).

Connect to the Time Capsule directly using the IP instead. From Finder select Go => Connect to Server and then enter: afp://123.123.123.123/ 

Substitute your own IP ofcourse!