Haven't done this before on the Fit, so needing a bit of advice. This on an '09 base model.
How difficult is it to get to the radiator drain petcock w/o removing the underbody plastic splash shield? Does it unscrew completely or stay in to drain? What size ID tubing goes on the drain fitting to keep it from running everywhere?

Do I have the refill and burp procedure right? Understand it can be a bit tricky sometimes:

Fill radiator and overflow bottle
Idle until fans come on a few times with rad cap off, heat set to high
Top up as coolant is drawn in when thermostat opens
Close radiator cap and allow to cool down 1-2 hours, then refill bottle to middle point

 

I haven't looked under a GE8 in a bit BUT there should be an access hole in the splash shield for the coolant to drain through and not touch/spill on anything if the car is level. If I remember right, you should be able to easily access the petcock (may need pliers to initially "free" it) by jacking up and supporting the front of the car. Once the petcock is loose, lower it down so that its even and let it drain out slowly enough so that the coolant does not get all over the splash shield (its an annoying mess with coolant replacement).

You're pretty much on the correct route in terms of procedure.

For adding/burning the system I use this funnel linked below...


...it features adapters that fits snug on the radiator so that the funnel will "self fill" coolant into the radiator as air escapes. In addition to that, there is a stopper that you insert in the funnel once done and there extra/unused coolant remaining inside which helps with keeping things nice and tidy.

I fill the coolant reserve tank then fill the radiator with that funnel installed until it is obvious that the radiator isn't taking in more coolant due to air pockets (you'll see what I mean when you do this). Once this happens, I start the car... Let it idle for a few minutes if it was a cold/initial start to warm up the engine oil... then HOLD the RPMs up at 3k for a minute or two and allow the car to idle for the same time period (check coolant level during these idle breaks).

Repeat this until the thermostat opens.

Once the thermostat is open allow the vehicle to idle for a few more minutes then shut the engine off and allow for the cooling system to have any additional air to escape.

 

For adding/burning the system I use this funnel linked below...


That's a nice set, a bit pricey though. If I were doing more often, say as a shop tech, certainly. Being that the Fit's system is so small, I figure one of these may work OK:

FloTool Radiator Funnel 10703: Advance Auto Parts

Since we're only dealing with a total of 1 gallon. Just pour slow, keep a bit in the neck like you said to go in as the level drops. Thanks for the tips, not something you do all that often, just wanna make sure I've got the basics right.

 

I just did this to mine today, along with an oil change. In addition to the radiator, there is a drain plug on the engine block which you should also drain. So it is a good idea to remove the splash shield. Not too difficult to do, but those damn plastic fasteners that Honda uses are crap. Ended up breaking three of them.

 

Go to your local Honda Parts dept. Mine gives them away for free. They get them as part of various assemblies and never use all of them. He must have 100 of them sitting there he has collected.

You can also buy them cheap on ebay.

 

Got it done yesterday, piece of cake. Friend has a drive-over work pit, easy access with a creeper. The petcock was much easier to get to than I thought. Drains perfectly thru a hole in the shield. Got almost 1 gal drained, didn't bother to do the block drain bolt, prob only a few oz left. For the refill, I put together a tapered funnel:

http://shop.advanceautoparts.com/p/flotool-super-multi-purpose-funnel-10712wr/9180013-P

with a short piece of clear tubing over the end, the OD of which fit snug inside the radiator neck. Slowly poured coolant, then squeezed upper hose which burped air pockets out. Got almost the full gallon in, filled the bottle to the max mark, then ran the engine until up to temp. Observed coolant flow at the upper hose, then shut off and put the cap on and allow to cool. So far it has pulled the level in the bottle down to the min mark. Will check it again, but don't expect it to drink much more. Surprised at how easy it was to get air out by just squeezing the upper hose.

 

You can get the EXACT clips on Amazon for either 10, 25, or 50 piece pack for about 2 or 3 dollars.