My thoughts?
I can't tell if flushing with tomatoes makes any difference as I never smoked them... LOL

Just feed them till harvest.

I guess that's lucas's way of saying. Well I wont say What I think it's saying, but I don't think it's very funny. Although I don't relay think much of flushing plants before harvest either.

I think if you give them a well balanced nutrient solution all the time in the first place, they will taste great. They build the flavor as they grow, not in the last 2 days or so before harvest. Even if you wanted to flush them before harvest, you would be flushing all the time because tomato's are continuously fruiting plants.

Hmmmm.....I've never smoked tomatos either. Nor have I actually ever harvested anything from a hydro garden. I'm still pretty new. Everything I've read says to replace nutrients with water + something for a final flush before harvest. The flushing all the time comment has occurred to me as well and I would suppose even with determinate varieties it would be difficult to time. I suppose I will just harvest a couple when ripe and decide then.

The only crop I'm aware of which people flush is MJ. Thus Lucas' comment.
I have heard people discuss flushing leafy greens before harvest, but the discussion was equally refuted/debated on both sides.
If you're growing them at a reasonable concentration, you don't need to flush a tomato system. I grow mine at around 800ppm. I don't grow at ultra high concentrations, so I can't speak to the need there.

Absolutely no need to flush except to occasionally flush the substrate/medium you are using to remove excess salts. Generally that's for denser media. In that use, it's usually referred to as leaching. One reason I have been told for "flushing" fruiting plants is to increase the amount of water in the plant to increase size for sale in the market. It doesn't add to flavor any more than flushing cukes in a ground garden does to get them bigger for the market. If they are for personal consumption or you have a good customer base that understands quality over quantity, there is no reason to try to increase water consumption by decreasing salt content. Also, it is my understanding that it is a myth that using sugars in the root zone will increase sugars in the fruit. That is the point of the molasses in hydro. In soil, it's to give a boost to microbes, where it has a somewhat legitimate purpose, though not necessarily a useful one. Bad microbes eat it up, too. You could do it for microbes in hydro, too, but it isn't exactly easy to control and you may wind up with a stinking mess and lots of hard work down the tubes.

Some call it "carbo load" in hydro because they think that the sugars will increase the sugars of the plant in significant quantities. Plants primarily load fruit with sugars from photosynthesis. Want more sugars? Optimize lighting.

There is another reason to flush. When you are ready to switch to a bloom formula, flush for a day or two with just water before you add the nutrient. It seems to speed up the transition. I'm guessing due to lack of nutrients. Also, if you want to rush ripening, I have flushed the substrate for that purpose for a few days. I don't know if there is any solid research out there, but it seems to work consistently for me on bell peppers. I keep some plants growing green bells and in another system I will push for ripening for early ripe fruits for salsa. The ones I starve always ripen faster, but the size of the fruits suffer quite a bit and so does the overall production. I wouldn't do it to push ripening tomatoes, though, for risk of BER.