After using the potty trainer a while, Chazz decides to graduate Chuckie to the toilet, using the Big Boy Potty Training Seat. But after noticing that Spike is using the tree to "do his business", Chuckie decides to follow suit, but Didi insisted that Chuckie uses the toilet. At this point, Tommy thought the rules have changed regarding the use of the tree as a "rest area". Therefore, the Rugrats decide to teach Spike to "relieve himself" the way humans do, first by using a diaper on Spike, then by having him use a toilet. As for Chuckie, he's afraid to go himself while everyone else is looking at him. (thetvdb.com)