You can actually remove the lower rubber channel by sliding the window part way and then lift one end of the channel out and pull it out. Sliding the glass back and forth may help. It can come out either way (left or right). Then the sliding glass drops down into the aluminum frame and you tilt it out. That exposes the window frame channel and lets you really clean it, and the weep holes. Then you can take that rubber channel with fuzzy surface and wash it in a bucket of suds and brush any dirt and sand* out. Put the glass back in, hold it up and slide the channel back in place underneath. You will need to push out the outside rubber seal lip a little to make it easier. It seemed hard the first time, but after I figured out how those things are put together, it was a snap. I am not sure if lubricating the channel is a good idea. (This is for Hehr windows, but they all must be similar.)
*)If there is any sand in the fuzz of the rubber channel, sliding the window may sound like fingernails on a chalkboard - awful. We old ones know what that was like!