there are several rules about where the chinese letters come from. One of them is the joining of meaning and sound. - sound similarity, like 可(ke)，河(he)，柯 (ke) three of them has differences like the root sound or the tone but finally they are similar. - Meaning relationship: finally 廁 refer to the room, so it needs a roof... actually, originally the traditional writing of factory is this one 廠 so taking it in mind for the construction of the letter, the concept of "factory" doesn't contribute at all.

If you want, you can remember it like this. "廁" is the initial form of "厕". In Ancient China, there are a few rooms in the yard, just similar to the Beijing 四合院. "广" means the most important room in this yard. "侧" means sideward, "亻" means a person. Similarly, "廁" means something beside the most important room in this yard. And the toilet is alway in the corner of the yard. So we could say it is beside the most important room. Anyway, please do not learn Chinese in this way if you wanna learn it fast and only for communication. However, if you want to study Chinese, this is absolutely the right way.

Not every simplified Chinese character can be understand directly from the appearance. Because they were simplified after the foundation of People's Republic of China for convenience. If you wanna study Chinese in this way, you have to find out the initial form of the Character and be familiar with ancient Chinese. http://www.zdic.net/z/16/zy/5395.htm This website could be useful for you to know more about the origin of the Chinese characters. I guess it would be too difficult for a beginner. Have fun :)

并不是每个汉字都可以从其组成结构看出它的意思，中华人民共和国成立之后，为了书写方便，对古汉字进行了简化，有的汉字经过从繁体到简体的过渡之后，已经看不出本来的象形意义了。可能"厕"字可以拆分解释，但是大多数中国人都不十分了解汉字的象形意义，只有少数研究古汉语的人才懂。 所以在初学汉语阶段，不必每个字都去按象形意义来记。

because toilet isn't just "厕", it's "厕所" and if you say "请问， 厕 在 哪儿？" the sentence will be incorrect which will make you exclaim "oh, Chinese language is so-o-o-o-o hard !!! even if i know the word toilet -- i still cannot find it !!!"