"越往下端越细的" can be translated into English as "tapering towards the lower/bottom end" or "becoming narrower towards the lower/bottom part".
Here are two example sentences to illustrate the usage:
1、 This vase has a tapering shape towards the lower end, which gives it an elegant look.
（这个花瓶越往下端越细，显得很优雅。）
2、 The tree trunk becomes narrower towards the bottom part due to natural erosion.
（由于自然侵蚀，这棵树的树干越往下端越细。）