I want to change the engine coolant in a 2005 Chevy Blazer 2wd with V6. However the radiator does not have a normal drain plug. There is a plastic nipple on the lower right side that is a molded part of the side tank that appears to be sealed on the inside. Is there a special (GM) tool and cap that will open then plug this nipple for cooling system maintanance?

https://www.justanswer.com/chevy/3pa5y-change-starter-1997-chevy-blazer-4wd-4door.html

Cassie, open the posted link for picture and location of plug.
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Theres no such thing as a diagram, here are the draining instructions, hope this helps...

1-Place a large drain pan beneath the radiator drain plug. The drain plug is located on the passenger side at the very bottom of the radiator on the engine side.

2-Make sure the engine is cool. Open the hood of the truck and remove the radiator cap.

3-Loosen the drain plug. On the 2000 Blazer, the drain plug is a wing-nut type of plug. Twist it with your fingers until the coolant begins to drain.

*To flush the block, once you have drained the radiator, run the engine for a bit untill the temp gauge goes up to normal, then the coolant will have been evacuated from the block. DO NOT leave the engine on, once it reaches normal temp, (this will happen quick) turn off right away, otherwise you'll be forking out a few hundred $$$ to fix the worped heads.
4-Tighten the drain plug with your fingers once the coolant has drained fully from the radiator. Remove the drain pan and dispose of the used coolant properly.
Some service stations will take and recycle your used coolant.
Hope this helps...

Read more: How to Drain a Radiator From a 2000 Chevy Blazer ' eHow.com http://www.ehow.com/how_6357264_drain-radiator-2000-chevy-blazer.html#ixzz1VS4RBufX

the drain valve is located on the back of the radiators plastic side tank, most models on the drivers side, u can't reach it from up top, get under the car and u will see it, a black plastic valve

You'll want to remove the radiator cap. On that tank, on the bottom toward the engine is a drain to unscrew. You might want to spray some WD-40 on the drain plug, to help get it unscrewed.

Regular Prestone or Peak Anti-Freeze. You should always pour it in the coolant tank, as the radiator needs coolant, it is drawn in from the coolant tank to the radiator, and also the reverse, so you only want to fill it up to the "FULL" level on the bottle. Recheck it after it's been driven.

there is a petcock at the bottom of the rad drain ti from there and use a antifreeze tester to check protection temp

As seen in this link: (copy & paste entire link) http://www.autozone.com/autozone/catalog/parts/partsProduct.jsp?skuDescription=Cooling+System+Parts+/+Radiator&categoryDisplayName=Cooling+%26+Heating&fromString=&itemIdentifier=832928_100118_0_94036&
productId=832928&sortType=&parentId=63-0&filterByKeyWord=&isSearchByPartNumber=&navValue=16300172&categoryNValue=&fromWhere=&itemId=172-0&displayName=Radiator&store=2953&searchText=&brandName=Cooling+System+Parts .....there is what you call a pipcock valve you can turn to open and drain your radiator. CAUTION: DO NOT ATTEMPT TO DRAIN WHEN HOT!!! Let engine sufficiently cool first.

Open the hood, and to the right you will see a big thick hose connected to the top of the radiator, if you look down the right hand side of the radiator, you will see a thin hose with the opening facing up at you and it is connected to the lower part of radiator, where there is a plastic wing nut like plug, which when loosened, allows the coolant flow to come out of the small hose, but make sure that the hose is pointed down, into a 2 gallon bucket, then loosen. Also, nothing will come out unless you take the cap off your radiator reserve which is that square-ish looking container filled with orange dex cool (not green) coolant.
hope this helps you,good luck