How often do you add smoke fluid to your engines?

I add smoke when they need it.  I don't know what pipette you're using, but it sounds like a lot of smoke fluid if it's the Lionel plastic one that comes in many engine boxes!  You're talking about 45-60 ml of smoke fluid, that's WAY more than you should need for any refill.  Other than the first refill, I use from 1/3 to 1/2 of the JT MegaSteam dropper for a refill, depending on the specific locomotive.  For MTH stuff with high smoke, it gets used up pretty fast, but I get good mileage from most of my TMCC/Legacy locomotives.

 

The Lionel pipette is 3.0 ml full scale. Mike R. recommends about half way up to the first (0.5 ml) line. So he should be putting in about 0.25 ml at a time...and is instead using a 4.5 ml to 6.0 ml. A lot. Seems like it should be running out the bottom of the engine.

I pretty much stick to about 0.25 ml to 0.5 ml at a time but don't run a long time, but it's usually a long time 'til when I run it again.

The Lionel Premium Smoke Fluid bottle comes with about 59 ml when factory full.

Slipped a decimal, but the point was valid.   I agree, I can't imagine that fluid is all going into the smoke units!

 

over night some fluid will evaporate.

Not that much will evaporate!  Besides, More than a pipette full will likely overflow many if not most smoke units.  One full Lionel plastic pipette is slightly more than two full droppers from the 2oz JT's MegaSteam bottles, that's too much for a single fill.  1 1/2 to 2 pipettes will surely overfill it!

 

When I have little to no smoke coming out of the loco.

When the smoke gets thin coming out of the stack I shut it down and let the unit cool down before adding 15 to 20 drops.

Before I run an engine.

Go to youtube and search Laidoffsick...he has some great videos on Legacy smoke units and other stuff.  Plus, he's a heck of a great guy.