I'm not sure what you're asking? The radiator drain bolt is under a little hatch that's attached to the bumper but I don't think that's what you're after. I don't think there is another drain bolt for the coolant that's leftover.
I just make it easy, just warm up the engine so the thermostat opens and flush it with water out of the drain plug from the radiator, then when I see clear water coming out, turn the motor off and let the rest of the water come out. Then pour in the fluid, bleed the system, and fill up the reserve tank. I only use honda coolent.
The new Honda antifreeze comes only in premixed form - so it's impossible to exchange the fluid completely by draining and refilling. But, with the engine running, you can drain the old fluid out of the top radiator hose (from the thermostat housing to a large bucket) while refilling with new coolant (thru the radiator cap). By warming the engine first (and introducing HOT flush water), the thermostat stayed open and expelled the old fluid at a moderate rate - slow enough to refill without panicking, yet fast enough to minimize mixing the new fluid with the old. It worked great - without removing the thermostat or opening the radiator drain petcock.
Here are the details:
Originally, I had replaced the coolant with "off-the-shelf" antifreeze. Then, I read that the anti-rust ingredients in off-the-shelf antifreeze are abrasive to the Water Pump (this debate can be found elsewhere). So, I wanted to start clean, by flushing-out the abrasive stuff and replacing it with Honda fluid. But draining the coolant via the petcock removes only half the coolant capacity. And, the cylinder block drain plugs are difficult to reach. And a "Coolant Flushing Kit" (using a "T" fitting and a garden hose) seemed difficult to install because the heater hoses are buried between the engine and the firewall. All these problems were solved by "flushing while running".
Here are some tips:
Use a clear plastic hose (any hardware store) so you can see the color of the fluid leaving the engine. I couldn't find a hose that would fit the nipple on the thermostat housing, so I disconnected the top hose from the radiator side, and used a nipple that converted to the size hose that I bought.
Use multiple buckets so you can dump one into the other before it overflows. This will also help you monitor the color of the fluid leaving the engine.
Turn the cabin heat to HOT during the flush / refill.
Introduce a few gallons of HOT clean water before introducing the Honda antifreeze. HOT water helps keep the thermostat open. I considered heating the new antifreeze in a tub of hot water, but it wasn't necessary.
After flushing with clear hot water, but before introducing the new antifreeze, let the engine to deplete most of the water from the radiator. This should help mimimize any mixing of fresh pre-mixed antifreeze with any flush water still in the radiator.
Don't forget to bleed any residual air from the system using the bleeder vent.
If you do this in your garage, don't forget to vent the exhaust pipe to the outside.
i'm not trying to flush the system. i am trying to remove all the fluids so i can pull the engine out. i just took the oil cooler off though and a lot of coolant came out through there so i may not even need to drain it from the block.
on a separate note i hope the oil cooler was the worst part of the process cause that thing was a pain in the ass. i finally gave up trying to pull the lines off and just cut em. there is absolutely no room.