I know this is an old link, oldie but goodie. I thought I would put my 2 cents in since I did it today. First, I would like to say how much I appreciate the knowledge I can get from this site. I have had the same luck with a former car owners club and two motorcycle clubs, which enabled me to do quite a few mods. I have the Ridgeline service manual, and together with this site was able to change all the fluids over the years and add a couple economical accessories. I bought it new in 07 and have managed to stay away from the dealer pretty much.
This job was harder than I thought it was going to be. The petcock on the radiator is very hard to access. I could not reach it from above, and the 3" access door on the bottom was not very friendly either. So I had to make up a tool, kind of like a slotted socket, out of a thin piece of pipe with a hole drilled in the end to insert a small rod, just to be able to turn the petcock. As for that drain fitting on the rear of the engine- that was really hard to reach also. I took off the right front wheel, put it up on jack stands and struggled to get a wrench on it and turn. By the way, it takes a 12 mm wrench or socket. I loosened it with a socket and then switched to a combination wrench after I got the hose in place. I picked up 4' of clear tubing at the hardware store for 40 cents a foot. Although the box said the tubing was 1/4" I.D. it was too tight. I reamed out the end to make the opening larger with a 17/64 drill bit and it fit good. But that was hard to reach and turn. The wrench barely fit. I did get out about what the service manual says- 1.65 gallons, and by the time I filled the radiator and overflow tank, it took almost the 2 gallons I bought. (I had 1 quart leftover). That funnel is available at your local NAPA store for $35, part number 24680, which is the updated version (although you don't need the updated peices- you only need the funnel, stopper, and Part C yellow fitting inside Part c radiator cap). It works really good. That was the only fun part of the whole job and the least time consuming. The fan came on real soon, so I let it run longer until it came on three times.
Last time, 5 years ago, I had the dealer flush the coolant. He charged me $159 and I noticed on the receipt there was only 1 gallon of coolant. So I am thinking he only did the radiator, not the engine block. Since coolant went up in price, I'm not sure what today's price would be. So I bought two gallons for $39.50 plus tax. It's really like buying only one gallon because it's half water, so the way I see it they are charging $39.50 per gallon! But I probably saved $100 by doing it myself, although it did take me most of the day when it was all said and done, but at least the whole job got done this time.