I have read through some other posts on different Triumphs, so the "secret" is to get the caliper above the resevoir in order to bleed correctly. Quesion is do you insert some sort of "disc duplicate" in order to not push the piston our of the caliper if it is removed from the wheel/disc to proceed with the bleeding procedure? Thanks for tricks/opinions/suggestions.
You can buy a bleeding tool for next to nothing. Worth every penny. https://www.aliexpress.com/item/32995225817.html
This is how I have done it. Suck in new Dot 4 using the pump on the caliper bleed nipple. Works pretty well. If you want to pump the brake leaver without pushing the pistons out a bit of wood works well. Another method I am planning to try is get a big ish syringe and push Dot 4 from the bottom up to the resovoir.
Just don't empty the brake reservoir. Empty just over half and add new do this a few times and hey presto job done. No need to do anything. But remember to hold the lever in and lock the brake between each refill. Joe.