This was because there weren't bathroom breaks for the speakers.
***snip***
Types of Filibusters
There are two types of filibusters. The traditional filibuster, which is not very common anymore. It was the kind which involved diapers, phone books, etc where Senators speak non-stop for hours upon hours. The other type of filibuster is the procedural filibuster (or in the opinion of this researcher, a make-believe, pretend filibuster), which has become more common in modern times. This is not really based on the idea of unlimited debate, but is based on the notion that 41 or more votes in the Senate can block a bill. The minority simply says 'We're filibustering this'. Since the majority doesn't really want to know where citizens with last names A through G in the Washington, DC area live, they reply 'Oh, alright...'. If they wanted to, the majority always has the option of saying 'Prove it!' and making them use a traditional filibuster. The procedural filibuster is a kind of a way of blocking a bulldozer without having to lie down in the mud, as the character Ford Prefect attempted in the book Hitchhiker's Guide to the Galaxy.
One advantage of the procedural filibuster is that it's much more dignified. The Senate can move on to other business sooner, instead of playing a high stakes parliamentary game of 'chicken'. However, though the victor on important issues is not decided by who has stronger bladders, the minority is better off with the procedural filibuster. It's impossible to break a procedural filibuster without a cloture motion (or by changing the rules, which would be ridiculously hard to do). However, many a traditional filibuster has been broken through waiting the minority out and clearing the Senate schedule (which the Senate Majority Leader can do). They have to give up at some point. They're only human.
Another disadvantage of the procedural filibuster is that it's more likely to be abused. As the filibuster becomes easier to do, there are more of them, and the minority stops using the procedure to kill especially offensive, controversial or radical legislation and just filibusters anything it doesn't like. However, the procedural filibuster does facilitate compromise, as it's easier to threaten to filibuster if you're prepared to filibuster, thus scaring the bejeezus out of the majority so they tone down their legislation to make it more moderate.
http://www.bbc.co.uk/dna/h2g2/A4814110