Hi we have a Draytek router 2862.
We have DrayTek WAN1 plugged directly in the WAN1 port as a Broadband line
on DrayTek WAN2 we want to attach a technicolor router, but only to allow the Draytek to have a WAN2

... is is possible, sustainable?

Yes this will work. 2 points to note:

• You'll need to use Routing Policies to define what traffic from which hosts should go down what WAN link

• The Technicolor router will either need to be put into a Bridge Mode or you'll have to live with a double NAT. There are some workarounds to help with the latter.