I don't have any Precisions with MXM. Water cooling one is definitely in the pipeline though, as soon as I can find a Zalman Reserator XT and mod the living shit out of it to make it more reliable and perform better.This ^ This ^ and This^ . Did I mention you should to this ^? A drain valve at the right spot will let you keep your machine upright, and save you both time and the expense of rolls and rolls of extra paper towels.
When I was still running a custom loop, I had both a drain and fill valve. I tend to over engineer and don't like a mess, so I put the fill valve at the high point in the loop so I could fill and "burp" air out easily. I'm by no means an expert, but it worked well for me.
If you really want to learn about custom loops by doing though, I suggest you set up a loop for one of those Precisions. Think of the challenge of fitting a block on a mobile CPU and an MXM card!
A voltmodded 940XM with a Reserator might hit 4 GHz stable lol