都 vs 也 in "连。。。都／也" structure I would like to learn when to use 都 and when to use 也 in the 连。。。都／也 structure.

My current understanding is that 都 is often used for positive sentences whereas 也 is generally used for negative sentences, e.g.

他 什么 都 吃，连 狗肉 都 吃。
我们 连 一 次 也 没 见 过。

However, I can see many exceptions to this 'rule'. Any more hints on when to use 都 or 也? Does it matter in general?

Thank you!
连...都... and 连...也... are interchangeable as a structure. In fact, in the structure 连...都..., 都, as an adverb, means 也! 

In your case, the sentence could be rephrased as 


  他什么都吃，连狗肉 也 吃。 我们连一次 都 没见过。


However, in the first sentence, 他什么都吃, 都 can not be replaced by 也. Here, 都 means 'all'.