Is it recommended to put a water separator in your fuel tank at the beginning of the year to help with any condensation that may have occurred in the tank? 

I run stabil, quikleen and seafoam year round (probably go a little overkill on both).

I have a 2006 merc. optimax if it matters (DFI)

I'm not saying it wouldn't hurt but I've never run one. My DFI Evinrude has a factory installed filter/seperator but other than that, I don't run anything else. When I take the Evinrude off and put one of my hotrod motors on, I don't use one. If I were to have a water/trash problem, I would clean the tank. You will never get enough condensation inside you're built in tank to ever have to worry about it. If water gets in there, it came from the gas pumps or some other source, not condensation.

I've been buying gas for vehicles since 1962 and trust me, I have on several occassions had the pumps put water in my tanks, so that does happen

Cool....thats what I wanted to hear!

Keep in mind, that because condensation is not a problem in one area, it can be a serious problem in others.

A fuel tank that has been taking in warm humid air may have a condensation problem on cool nights. The moisture in the air in the tank will condense on the cool metal inner surface of a tank. It will be somewhat less of a problem on plastic, or fiberglass tanks.

What may or may not occur in one area of the country does not necessarily apply in other areas.

That's why refilling your fuel tanks after an outing greatly reduces the problem. Filling the tank drives the moisture laden air out.

Fill your fuel tanks on the way home, and you'll be less likely to experience condensation problems. Warm humid days, cold nights, and a less than full tank is a formula condusive to condensation.

Eliminating a problem is preferable to treating the problem.

Also remember for many years gas was 100% gas. Ethanol changes the game from what I have read(ethanol absorbs moisture). I recently installed a fuel/water separator on my bassboat because pure gas is getting a little harder to find. I can locate pure gas locally but on a recent trip to Florida I knew it would not be possible. Although I have never had a problem, a $30 separator, which is easy to install, is pretty cheap insurance........Al