Get underneath it and take the pipes apart and clean them out and put it all back together again and test it for leaks - or - call in a plumber and ask him to do it for you.
The "clogging" will be due to the stuff that goes down the drain hole - hot fat is particularly bad because is cools and sets into a solid mass.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix plumbing.