Clearing Buffers

I have a project, whereby we're using DirectPlay to create a multiplayer game. However, we're facing a problem.

As the duration of the game increases, so does memory usage. We have heard that this problem is due to the buffers being filled up. How do we reduce buffer occupation?

We monitored the memory usage through the Windows Task Manager until Windows had to auto-increase the virtual memory. All this happened on a PC with 128MB RAM!

Anybody can help us out?

What kind of buffers?

We currently using direct X 8. In our server, we got a timer that send data to client every second. So now right, we think the memory is being used to keep all the data the line up in the buffer. Which means the data that cannot send during that time and keep it in a line. So now how can we reduse the usage on memory or clear the buffer? For the buffer type, if im not mistaken, its a string.