To follow a blog on Tumblr using RSS, follow the following steps:
1: take the username or "URL" of the blog you want to follow. For example, let's say we want to a blog named doingitfortheexposure. This blog doesn't have a custom template on Tumblr, so its URL is:
https://www.tumblr.com/doingitfortheexposureAbove, the part we care about, doingitfortheexposure, is part of the URL path.
If it had a custom template, its URL could be:
https://doingitfortheexposure.tumblr.com/In this case, the part we care about, doingitfortheexposure, is the subdomain.
Some blogs hosted on Tumblr may have custom domain names, e.g. example.com. To get their RSS feed, we'll have to do something a bit different.
2: take the username of the blog and use it as subdomain for tumblr.com, then make the URL path /rss. For example:
https://doingitfortheexposure.tumblr.com/rssThis is the URL you should give to your RSS client.
If the Tumblr blog has a custom domain, it might not be clear what its username on Tumblr is. The URL path /rss on their custom domain name should work nevertheless.
https://example.com/rss